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AGRICULTURAL 
BACTERIOLOGY 


Ube  Century  Bgricultural  Series 

AGRICULTURAL 
BACTERIOLOGY 

FOR  STUDENTS  IN 
GENERAL  AGRICULTURE 


BY 

H.  L.  RUSSELL 

Dean  of  the  College  of  Agriculture 
University  of  Wisconsin 

AND 

E.  G.  HASTINGS 

Professor  of  Agricultural  Bacteriology 
The  College  of  Agriculture 
rersily"ori¥4«;onsin 

ILLUSTRATED 


NEW  YORK 

THE  CENTURY  CO. 

1921 


Copyright,  1921,  by 
The  Century  Co. 


FOREWORD 

The  art  of  agriculture  has  long  been  practised,  but  the 
science  of  agriculture  is  of  comparatively  recent  origin. 
This  science  rests  upon  the  fundamental  sciences — chem- 
istrj',  physics,  and  biology.  One  phase  of  biology,  bac- 
teriology, has  within  the  last  three  decades  assumed  a  most 
important  relationship.  The  early  researches  of  Pasteur, 
Koch,  and  their  successors  opened  the  field  of  inquiry  as 
to  the.  causation  of  animal  disease.  More  recently,  exact 
knowledge  of  the  influence  of  microorganisms  on  soil  pro- 
cesses, on  dairying,  and  on  foods  in  general  has  been  greatly 
extended.  It  is  of  the  utmost  importance  for  the  farmer 
and  the  student  of  agriculture  to  have  a  proper  conception 
of  these  relations. 

The  purpose  of  the  text  here  presented  is  to  give  to  the 
reader  and  to  the  student  the  essential  facts  concerning  the 
relation  of  microorganisms  to  daily  life,  and  especially  to 
that  of  the  farm,  without  a  confusing  mass  of  detail,  both 
chemical  and  biological,  the  presentation  of  whieh  often 
hides  the  essential  information  the  student  should  gain. 
The  terminology  is  simple.  Descriptions  of  specific  or- 
ganisms have  been  avoided;  and,  in  general,  the  various 
phases  of  the  subject  are  presented  in  their  broad  outlines 
in  order  to  acquaint  the  student  with  the  fundamental  prin- 
ciples, which  can  be  applied  to  subjects  not  considered. 

A  full  conception  of  the  relation  of  microorganisms  to 
agriculture  can  not  be  gained  without  working  with  them  in 
the  laboratory.  Without  such  experience  the  organisms 
remain  intangible  to  the  student.    Much  can  also  be  done 


^oTfc 


VI 


FOREWORD 


by  the  teacher  in  the  class-room,  through  the  use  of  more 
extended  illustrative  material  than  it  is  possible  to  give  in 
the  text,  and  through  examples  of  the  practical  application 
of  the  organisms,  to  increase  the  interest  of  the  student  in 
this  subject  that  has  so  many  points  of  contact  with  the 
daily  life  of  every  individual. 


CHAPTBE 


CONTENTS 

PART  I 
PROPERTIES  OF  MICROORGANISMS 


I    The  Role  op  Microorganisms 3 

Constructive  agencies.  Destructive  agencies. 
Decomposition 

II    The  Development  of  Bacteriology  ....      7 
Discovery  of  bacteria.     Spontaneous  genera- 
tion.    Pasteur.     Aniline  dyes.     Koch  and  the 
gelatine  plate 

III  The  Morphology  op  Microorganisms  ....     12 

Morpliology  of  bacteria.  Morphology  of 
yeasts.    Morphology  of  molds.     Protozoa 

IV  Cultivation   and   Study   op  Bacteria,  Yeasts, 

AND  Molds 33 

Culture  media.  Liquefiable-solid  media.  Ster- 
ilization. Isolation  of  pure  cultures.  Quan- 
titative methods.  Microscopic  examination. 
Systematic  study  of  bacteria 

V    Physiology  op   Microorganisms 48 

Moisture.  Temperature.  Oxygen.  Reac- 
tion. Light.  Chemicals.  Food.  Metabiosis. 
By-products.  Classes  of  organic  matter. 
Distribution  of  microorganisms 

PART  II 

SOIL  BACTERIOLOGY 

VI    The  Relation  of  Microorganisms  to  Soil  Fer- 
tility  69 

Unavailable  and  available  plant  food.     Soil 


viii  CONTENTS 

CHAPTER  PAGB 

as  a  culture  medium.  Moisture  and  air. 
Temperature.  Reaction.  Number  of  organ- 
isms in  soil 

VII    The  Decomposition  of  Organic  Matter  in  the 

Soil  Humus 78 

VIII     The  Cycle  of  Carbon 83 

Cellulose  decomposition.  Retting.  Oxida- 
tion of  hydrogen  and  methane 

IX     The  Action  of  Bacteria  on  the  Minerals  of 

the  Soil 87 

Calcium.  Phosphorus.  Potassium.  Sulphur. 
Iron 

X     The  Cycle  of  Nitrogen 94 

The  nitrogen  of  the  soil.  Ammonification. 
Nitrification.  Conservation  of  nitrogen.  Ni- 
trate deposits.     Denitrification 

XI    Barnyard  Manures  and  Sewage  Disposal  .     .  107 
Manures.     Sewage  Disposal 

XII     The  Fixation  of  Nitrogen 117 

The  fixation  of  nitrogen.  Leguminous  plants. 
Inoculation  of  soil 


PART  III 
THE  RELATION  OF  MICROORGANISMS  TO  FOOD 

XIII     The  Contamination  of  Foods 135 

Factors  governing  decomposition.  Contami- 
nation of  milk:  from  interior  of  udder,  from 
air,  from  the  animal.  Influence  of  the  milker. 
Contamination  from  utensil.  Cleaning  of 
milk  utensils.  Contamination  from  factorj^ 
by-products.  Straining  and  clarifying  milk. 
Influence  of  feed  on  contamination  of  milk. 
Contamination  of  other  foods  than  milk 


CONTENTS 


IX 


CHAPTER 

XIV 


XV 


XVI 


XVII 


XVIII 


XIX 


The  Contamination  op  Foods  with  Pathogenic 

Bacteria 154 

Bovine  tuberculosis.  Septic  sore  throat  and 
garget.  Typhoid  fever.  Diplitheria  and 
scarlet  fever.  Influence  of  bacterial  content 
on  healthfulness.  Infant  mortality.  Poison- 
ous foods 

The  Preservation  op  Foods 168 

Purification  of  water.  Inhibition  of  micro- 
organisms. Desiccation.  Concentration. 
Preservatives.  Organic  acids.  Silage.  Low 
Temperature.  Eggs.  Heat.  Pasteurization 
of  milk.     Sterilization 

The  Fermentations  Occurring  in  Food  Prod- 
ucts       186 

Acid  fermentation  of  milk.  Sweet  curding 
of  milk.  Butyric  fermentation.  Slimy  fer- 
mentation. Alcoholic  fermentation.  Vine- 
gar.    Bread 

The  Relation  op  Microorganisms  to  Butter  and 

Cheese 202 

Acid-fermentation  and  flavor  of  butter.  Pas- 
teurization of  cream.  Flavor  of  butter 
substitutes.  Decomposition  of  butter.  Ab- 
normal flavors  in  butter.  Cheese-making. 
Cheddar  cheese.  Gassy  cheese.  Swiss  cheese. 
Mold-ripened  cheese.     Soft  cheese 

The  Bacteriological  Control  op  Foods  .      .     .  215 
Municipal  control  of  milk.     Grades  of  Milk. 
Certified    milk.     Pasteurization     of     market 
milk 

PART  IV 

TRANSMISSIBLE  DISEASES 

The  Relation  op  Microorganisms  to  Diseases 

OP   Animals 239 

The  Communicable  diseases.     Infection.     Ex- 


f  CONTENTS 

IHAPTER  PAGE 

ternal  defenses.  Internal  defenses.  Im- 
munity. Active  and  passive  immunity. 
Persistence  of  immunity.  Exit  of  organisms 
from  the  body.  Necessity  for  correct  diag- 
nosis 

XX    Anthrax,  Blackleg,  Hemorrhagic  Septicemia, 

AND  Corn-Stalk  Disease 252 

Anthrax.  Infection.  Symptoms.  Lesions. 
Vaccination.  Disposal  of  carcasses.  An- 
thrax in  man.  Blackleg.  Symptoms.  Vac- 
cination. Hemorrhagic  septicemia.  Corn- 
stalk disease 

XXI    Tuberculosis 269 

Animals  affected.  Distribution.  The  tu- 
bercle bacillus.  Infection.  Lesions.  Distri- 
bution of  the  tubercle  bacillus.  Infection  of 
the  herd.  Detection  of  tuberculosis.  Free- 
ing the  herd  from  tuberculosis.  Vaccina- 
tion. Tuberculosis  of  hogs.  Avian  tubercu- 
losis.    Joline's  disease 

XXII    Texas  Fever,  Contagious  Abortion,  and  Foot- 

AND-MouTH   Disease 295 

Texas  fever.  Eradication.  Immunization. 
Contagious  abortion.  Detection.  Control, 
and  prevention.  Foot-and-Mouth  disease. 
Nature  of  the  disease 

XXIII  Rabies  and  Actinomycosis 311 

Rabies.  Symptoms.  Diagnosis.  Preventive, 
treatment.  Actinomycosis.  Symptoms. 

Treatment 

XXIV  Glanders  and  Tetanus 320 

Glanders.  Distribution.  Symptoms.  De- 
tection. Tetanus.  Symptoms.  Preventive 
measures 


CONTENTS 


XI 


XXV    Hog  Cholera '6Z6 

Symptoms.  Lesions.  Prevention.  Protec- 
tive treatment 

XXVI    Diseases  op  Fowls 340 

Chicken  cholera.  Roup.  Fowl  typhoid. 
White  diarrhea 

XXVII    Bacterial  Diseases  op  Plants 34G 

Fenr  blight.  Cabbage  rot.  Wilts.  Galls  or 
tumors 

XXVIII    Disinfection 351 

Natural  agencies.  Chemical  disinfectants. 
Lime.  Carbolic  acid.  Coal  tar  disinfectants 
Formaldehyde.  Corrosive  sublimate.  Sul- 
phur. Calcium  hypochlorite.  Ferrous  sul- 
phate.    Copper  sulphate.     Disinfection 

Index 363 


LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

1.  Forms   of   Bacteria 13 

2.  Cocci 14 

3.  Large  Bacilli 14 

4.  Small  Bacilli 15 

5.  Spirilla 15 

6.  Spirilla 16 

7.  Spores 16 

8.  Spores 17 

9.  Arrangement  of  Cocci 18 

10.  A   Streptococcus 19 

11.  Bact.  Anthracis 19 

12.  A  Tetracoccus 20 

13.  Capsules 21 

14.  Yeasts 27 

15.  Spore-formation  by  molds 30 

16.  A  Plate  Culture 39 

17.  Effect  of  Acid  on  Bacteria  and  Yeasts 54 

18.  Effect  of  Light 55 

19.  Enzyme  Action 57 

20.  Etching  of  Marble  by  Plant  Roots 88 

21.  Effect  of  Nitrifying  Bacteria  on  the  Growth  of  Barley  .   101 

22.  A  Septic  Tank 112 

23.  The  Tile  Drain  of  a  Sewage  Purification  System  .      .      .   115 

24.  Nodules  on  Soy  Beans 121 

25.  Effect  of  Inoculation  on  Alfalfa 123 

26.  Effect  of  Inoculation  on  Peas 126 

27.  Effect  of  Inoculation  on  Sweet  Clover 128 

28.  The  Cycle  of  Nitrogen 131 

29.  A  Section  of  an  Udder 138 

30.  Contamination  from  the  Air     ........   140 


xiv  ILLUSTRATIONS 

FIG.  PAGE 

31.  Dirt  Tests 141 

32.  Bacteria  on  Hairs 142 

33.  A  Dirty  Stable 143 

34.  A  Clean  Stable 144 

35.  Sanitary  Milk  Pails 145 

36.  Typhoid  Fever  Spread  by  Milk       . 160 

37.  Typhoid  Fever  Spread  by  Water 161 

38.  Protection  of  a  Well 162 

39.  A  Home-Made  Pasteurizer 182 

40.  Ropy  Milk 192 

41.  Gassy  Cheese 211 

42.  Anthrax 257 

43.  Tubercular   Omentum 274 

44.  A  Tubercular  Spleen 275 

45.  Buying  Tuberculosis 277 

46.  Tuberculosis  Spread  by  Creamery  By-products  .      .      .  278 

47.  A  Tubercular  Animal 280 

48.  A  Tubercular  Animal 281 

49.  Injecting  Tuberculin  . 283 

50.  Reaction  Curves  in  the  Tuberculin  Test 285 

51.  Avian  Tuberculosis 291 

52.  Avian  Tuberculosis 292 

53.  Texas  Fever 298 

54.  Foot-and-Mouth  Disease 307 

55.  Foot-and-Mouth  Disease 308 

56.  Foot-and-Mouth  Disease 309 

57.  Actinomycosis 318 

58.  Glanders 321 

59.  Glanders 322 

60.  Hog  Cholera 330 

61.  Hog  Cholera 331 

62.  Roup 343 

63.  Pear  Blight 347 


PART  I 
PROPERTIES  OF  MICROORGANISMS 


AGRICULTURAL 
BACTERIOLOGY 

CHAPTER  I 
THE  ROLE  OF  MICROORGANISMS 

Animate  nature  is  commonly  divided  into  two  great 
groups:  the  plants  and  the  animals.  It  is  possible,  how- 
ever, to  make  the  division  of  life  along  other  lines  than 
form  and  function.  Every  living  form  must  have  building 
material;  the  various  chemical  elements  that  are  essential 
for  its  structure  must  be  available  in  fitting  combinations. 
Every  living  form  must  also  have  energy ;  for  work  is  being 
done  by  even  the  simplest  forms  of  life,  and  without  energy 
no  work  is  possible.  The  sole  source  of  energy  for  our 
world  is  the  sun.  The  energy  is  transmitted  in  some  inex- 
plicable way  through  the  space  that  separates  the  earth 
from  the  sun. 

One  group  of  living  organisms  is  able  to  receive  directly 
this  radiant  energy,  and  to  use  it  in  the  work  of  growth  and 
development.  This  power  is  limited  to  those  forms  that  are 
provided  with  the  compound  known  as  chloropliyl,  the  sub- 
stance that  gives  to  the  higher  plants  their  green  color. 
They  obtain  their  building  materials  from  the  soil,  the 
water,  and  the  air,  in  compounds  that  contain  but  little  or 
no  energy.  They  combine  these  simple  compounds  into 
complex  forms  that  contain  a  great  store  of  energy.  Thus 
the  plant  uses  as  food  carbon-dioxide,  water,  oxygen,  ni- 

3 


4      AGRICULTURAL  BACTERIOLOGY 

trates,  phosphates,  and  sulphates,  and  forms  from  them 
all  of  the  varied  substances  found  in  its  tissues — the  woody 
fiber,  the  sugars,  the  starches,  the  fats,  the  gums,  the  waxes, 
and  the  proteins.  The  green  plants  are  builders  of  organic 
matter  and  storers  of  energy.  They  represent  the  construc- 
tive or  the  synthetic  group. 

Living  forms  that  do  not  possess  this  wonderful  energy- 
receiving  and  -utilizing  compound,  chlorophyl,  can  not  use 
the  radiant  energy  of  the  sun  directly,  but  must  rely  upon 
that  which  the  green  plant  has  stored  in  its  structure. 
These  forms  use  vegetable  matter  as  food,  and  obtain 
therefrom  their  building  materials  and  the  energy  neces- 
sary for  all  their  life  processes.  They  utilize  the  energy  and 
leave  behind  simpler  types  of  compounds  than  those  in- 
gested. They  break  down  vegetable  matter,  and  are  to  be 
classed  as  destructive  agents,  or  as  analytic  factors.  The 
animal  that  lives  upon  the  tissues  of  another  animal  is  still 
relying  upon  the  green  plant  for  its  food  and  energy.  It 
is  to  be  seen  that  the  basis  of  classification  is,  whether  the 
energy  needed  by  the  organism  is  obtained  directly  from 
the  sun,  or  indirectly  through  the  medium  of  another  or- 
ganism. 

Destruction  of  man-made  structures  is  as  necessary  as  is 
the  building  thereof,  and  so  it  is  in  nature.  The  supply  of 
plant  food  is  limited,  and  it  is  essential  that  the  elements 
in  vegetable  matter  be  returned  to  a  form  that  permits  of 
use  by  another  plant.  This  is  the  work  of  the  destructive 
group.  The  green  plant  furnishes  to  all  other  forms  of 
life  food  and  energy.  They,  in  their  turn,  supply  the  green 
plant  with  food.  Each  group  is  absolutely  dependent  on 
the  other  for  its  continued  existence. 

Not  all  the  members  of  the  destructive  group  are  animals. 
In  it  are  placed  many  forms  that  every  one  recognizes  as 
plants,     They  are  devoid  of  chlorophyl,  ^n(l  demand  the 


THE  ROLE  OP  MICROORGANISMS  5 

same  kind  of  food  as  does  the  animal ;  their  food  must  sup- 
ply them  with  both  buildin^?  materials  and  energy.  The 
term  *^ fungi"  or  *^ fungus  plants"  is  applied  to  them.  One 
does  not  think  of  the  animals  as  agents  in  the  destruction 
of  organic  matter,  for  our  interest  in  them  is  wholly  along 
other  lines.  The  waste  products  of  animal  life  are  very 
simple  chemical  compounds.  Some  of  the  fungus  plants 
change  their  food  relatively  little  as  far  as  its  chemical 
complexity  and  energy  content  is  concerned.  Their  by- 
products are  almost  as  complex  as  is  the  food  itself,  and  in 
many  instances  possess  economic  value. 

The  destructive  work  of  animals  and  of  the  fungus  plants 
is  included  under  the  term  decomposition.  Other  terms, 
such  as  fermentation,  decaijy  putrefaction^  and  rotting,  are 
synonymous.  Usually,  however,  these  expressions  are  ap- 
plied to  the  decomposition  of  certain  chemical  substances, 
or  to  a  particular  type  of  decomposition;  for  example,  one 
says  that  milk  ferments  and  that  meats  putrefy. 

The  greater  part  of  the  decomposition  of  organic  matter 
is  occasioned  by  fungus  plants  of  microscopic  size  that  find 
their  home  in  the  soil  and  in  the  water.  The  body  of  an 
animal  is  buried;  within  a  short  time  it  completely  disap- 
pears. An  immense  amount  of  waste  organic  matter  may 
be  placed  in  a  stream — as,  for  example,  in  the  great  drain- 
age canal  that  receives  the  sewage  of  Chicago.  Before  the 
stream  that  receives  the  effluent  of  the  drainage  canal 
reaches  central  Illinois,  the  organic  matter  has  completely 
disappeared  under  the  influence  of  the  microscopic  life  of 
the  water. 

From  this  organic  matter  are  formed  carbon-dioxide, 
water,  sulphates,  phosphates,  and  nitrates.  From  organic 
matter  minerals  have  been  formed;  therefore  the  term 
mineralization  is  often  applied  to  the  process.  An  element 
passes  from  the  soil,  the  water,  or  the  air  into  the  green 


6  AGRICULTURAL  BACTERIOLOGY 

plant,  and  is  built  into  some  one  of  its  compounds.  These 
are  used  by  some  member  of  the  destructive  group,  or  more 
commonly  by  a  series  of  members  of  this  group,  with  the 
result  that  the  element  becomes  again  available  to  the  green 
plant. 

This  passage  of  the  elements  from  one  form  of  life  to 
another  is  called  the  cycle  of  the  elements.  An  atom  of 
carbon  may  be  in  the  air  to-day  in  the  form  of  carbon- 
dioxide;  to-morrow  it  may  be  in  a  sugar  molecule  of 
a  plant ;  the  next  day  in  the  tissues  of  an  animal ;  and  the 
succeeding  day  it  may  be  again  present  in  the  air  in  a  mole- 
cule of  carbon-dioxide;  ready  for  another  of  its  ceaseless 
passages,  carrying  with  it  a  supply  of  energy  for  the  animal 
and  the  fungus  plant. 

The  chief  agents  in  the  decomposition  of  organic  matter 
are  the  protozoa;  or  simple  animal  forms,  and  the  simple 
plant  forms,  which  include  the  bacteria,  the  yeasts,  and  the 
molds.  The  term  microorganism  is  often  applied  to  these 
various  types,  and  microbiology  to  their  study.  It  is  with 
these  forms  that  this  volume  treats,  and  especially  with 
the  ways  in  which  they  influence  the  life  of  man.  He  meets 
them  in  the  soil  he  tills ;  he  makes  use  of  them  in  the  prep- 
aration of  foods  and  products  of  industrial  value ;  he  is  con- 
stantly striving  to  protect  his  food  supplies  from  their  ac- 
tion, and  to  protect  himself  and  his  animals  from  the 
diseases  that  they  cause.  They  present  themselves  to  him 
at  every  moment  of  his  life,  to  his  benefit  or  his  injury. 
He  must  employ  them,  and  fight  them,  either  conscious  or 
unconscious  of  the  nature  of  his  acts ;  and  he  who  has  intel- 
ligent acquaintance  with  them  will  certainly  fare  far  bet- 
ter than  one  ignorant  of  the  part  they  play.  A  knowledge 
of  the  role  of  microorganisms  in  nature  is  as  essential  as 
knowledge  concerning  the  higher  plants  and  animals. 


CHAPTER  IT 
THE  DEVELOIWIENT  OF  BACTERIOLOGY 

Discovery  of  bacteria. — The  study  of  bacteria  is  one  of 
the  most  recent  developments  of  biologic  science.  The  facts 
that  had  been  gathered  concerning  the  bacteria  were  not 
grouped  into  an  independent  phase  of  biology  until  about 
1880.  It  was  not  until  1882  that  the  new  science  received 
its  name,  bacteriology.  The  bacteria  had  first  been  seen 
in  1688  by  Leeuwenhoek.  Apparently  he  was  the  first  to 
use  an  instrument  of  sufficient  magnifying  power  in  such  a 
way  as  to  make  the  bacteria  visible. 

The  compound  microscope  was  first  made  by  Johannes 
Janssen  and  his  son,  in  Holland,  in  1590.  The  objects  to 
be  examined  by  such  an  instrument  were  illuminated  by 
light  coming  from  above,  and  reflected  from  the  surface 
of  the  object  into  the  lens  of  the  microscope,  and  thence  to 
the  observer's  eye.  With  such  an  arrangement  the  bacteria 
could  not  be  seen.  Leeuwenhoek  used  a  simple  microscope 
in  his  work,  of  lower  power  than  others  had  employed.  He, 
liowever,  examined  his  objects  by  placing  them  between  the 
source  of  light  and  his  lens:  he  used  transmitted  light,  or 
the  kind  one  uses  when  he  wishes  to  determine  the  free- 
dom of  a  liquid  from  suspended  matter,  and  places  it  be- 
tween his  eye  and  the  window.  The  solid  objects  refract 
the  rays  of  light,  and  thus  their  presence  in  the  liquid  is 
made  evident  to  the  eye.  This  simple  modification  of  his 
microscope  made  Leeuwenhoek  the  discoverer  of  many  mi- 
croscopic objects,  among  them  the  yeasts  and  the  bacteria. 
He  is  frequently  called  the  father  of  microscopy. 

7 


8      AGRICULTURAL  BACTERIOLOGY 

Decomposition  and  its  cause. — From  1683  to  1850  little 
was  learned  concerning  the  importance  of  the  bacteria  in 
nature.  The  biologists  of  those  days  were  more  interested 
in  classifying  and  naming  the  various  plants  and  animals 
than  in  studying  what  they  were  able  to  do.  They  were 
interested  in  morphology  rather  than  in  physiology. 

It  had  been  known  to  man  ever  since  he  attempted  to 
preserve  plant  or  animal  matter  that  change  in  it  was  in- 
evitable. The  microscope  revealed  in  decomposing  material 
an  immense  number  of  microorganisms,  among  which  the 
bacteria  predominated.  It  was  believed  by  many  that  these 
organisms  were  the  cause  of  the  decomposition.  Justus  yon 
Liebig,  the  founder  of  organic  and  agricultural  chemistry, 
believed  that  decomposition  was  purely  a  chemical  process 
that  in  some  way  occurred  in  matter  brought  in  contact  with 
the  decomposing  material.  He  was  the  dominant  figure  in 
the  chemical  world  from  1840  to  1860,  and  when  he  stated 
that  'Hhose  who  pretend  to  explain  the  putrefaction  of 
animal  substances  by  the  presence  of  microorganisms  reason 
very  much  like  a  child  who  would  explain  the  rapidity  of 
the  Rhine  by  attributing  it  to  the  violent  motion  imparted 
to  it  in  the  direction  of  Bingen  by  the  numerous  wheels  of 
the  mills  of  Mayence,"  there  were  few  bold  enough  to  con- 
tradict him,  and  none  whose  reputation  carried  conviction. 

Spontaneous  generation. — Numerous  experiments  had 
shown  that  an  infusion  of  meat  could  be  boiled  for  some 
time  and  sealed  immediately  thereafter  in  the  vessel  in 
which  it  had  been  heated,  and  yet  it  would  often  undergo  de- 
composition, and  would  be  found  teeming  with  microscopic 
life.  Such  experiments  had  given  rise  to  what  seems  now 
a  curious  theory,  that  of  spontaneous  generation  of  life; 
that  is,  the  creation  of  life  from  dead  matter.  The  scien- 
tists of  those  days  could  not  imagine  that  any  living  form 
could  endure  the  temperature  of  boiling  water  for  even  the 


DEVELOPMENT  OF  BACTERIOLOGY  9 

briefest  period  of  time.  The  infusion  of  meat  had  been 
protected  from  the  entrance  of  bacteria  after  it  had  been 
heated;  therefore  it  was  believed  the  forms  found  in  the 
decomposing  infusion  must  have  arisen  in  some  way  from 
the  lifeless  material. 

Many  experimenters  tried  to  disprove  this  theory. 
Schultze,  in  1836,  heated  infusions  to  the  boiling-point,  and 
the  air  tliat  entered  his  flasks  when  removed  from  the  fire 
was  passed  through  strong  acid  or  alkali.  In  1837,  Schwann 
passed  the  air  that  entered  the  flasks  through  tubes  heated 
by  a  direct  flame.  Schroeder  and  von  Dusch,  in  1853, 
plugged  the  tubes  leading  from  the  flasks  with  cotton  wool, 
which  filtered  the  air  as  it  was  drawn  into  the  flasks  when 
they  cooled.  Usually  infusions  thus  treated  did  not  decom- 
pose. 

The  adherents  of  the  theory  claimed  that  the  exposure  of 
air  to  the  high  temperature  of  the  heated  tube,  to  acid  or 
alkali,  or  even  to  cotton  wool,  removed  some  life-maintaining 
principle  therefrom.  It  was  not  possible  by  such  experi- 
ments to  disprove  the  theory.  In  1860,  the  Paris  Academy 
of  Science  ottered  a  prize  for  an  attempt  to  throw  new  light 
by  suitable  experiments  on  the  question  of  spontaneous 
generation. 

Pasteur,  the  father  of  bacteriology. — Louis  Pasteur  was 
born  in  the  Jura  district  of  France  in  1822.  He  was  a  dili- 
gent student  of  chemistry,  and  became  interested  in  the  ef- 
fect of  certain  crystalline  substances  and  their  solutions  on 
polarized  light.  Among  the  substances  he  studied  was  tar- 
taric acid  and  its  salts,  products  of  one  of  the  great  fermen- 
tation industries,  the  wine  industry.  In  1854  he  was  made 
a  member  of  the  Faculty  of  Sciences  in  the  University  of 
Lille,  a  great  industrial  city.  He  began  the  study  of  the 
manufacture  of  alcohol  from  beet-sugar.  In  1857  he  read 
a  paper  on  the  lactic-acid  fermentation.     He  had  discovered 


10  AGRICULTURAL  BACTERIOLOGY 

in  sour  milk  a  trace  of  grayish  substance,  and  had  proved  it 
to  be  a  ferment  of  milk.  He  had  before  him  one  of  the 
most  important  of  the  bacteria.  This  work  was  the  begin- 
ning of  the  new  science  of  bacteriology. 

Pasteur  accepted  the  challenge  of  the  Paris  Academy, 
and  on  April  7,  1864,  he  gave  his  results  to  the  world  in  a 
famous  lecture  at  the  Sorbonne.  He  showed  that  if  any 
solution  containing  organic  matter  is  heated  long  enough, 
and  protected  from  the  microorganisms  in  the  air,  it  will 
remain  unaltered.  He  avoided  the  objections  that  had  been 
urged  against  the  experiments  of  others  by  allowing  air  to 
pass  in  and  out  of  his  flasks  through  long  curved  tubes,  on 
the  walls  of  which  all  dust  and  bacteria  would  be  deposited. 
He  showed  for  all  time  that  life  comes  from  life,  that  every 
form  is  the  progeny  of  preexisting  forms  of  like  nature. 

The  importance  of  this  work  of  Pasteur  can  not  be  over- 
estimated, for  it  led  him  to  continue  the  study  of  microor- 
ganisms until  his  death,  in  1895.  Pasteur's  influence  on  the 
material  side  of  human  life  has  probably  been  greater  than 
that  of  any  other  man. 

Aniline  dyes. — The  discovery  of  the  bacteria  by  Leeu- 
wenhoek,  and  the  recognition  of  their  relation  to  decompo- 
sition by  Pasteur,  are  two  great  landmarks  in  the  history  of 
bacteriology.  Another  was  the  accidental  discovery  of  the 
aniline  dyes  by  Perkin  in  1856.  The  recognition  of  the  bac- 
teria, as  they  occur  in  many  places,  especially  in  the  fluids 
and  tissues  of  the  animal  body,  is  impossible  unless  they 
can  be  difl'erentiated  by  stains  from  the  other  materials. 
The  aniline  dyes  were  first  used  for  the  staining  of  bacteria 
by  Weigert  in  1876. 

Another  great  advance  in  the  progress  of  the  science  was 
the  development  by  Robert  Koch,  a  German  physician,  of 
a  method  of  separating  one  kind  of  bacteria  from  other 
kinds  with  which  it  might  occur.     His  work  enables  the 


DEVELOPMENT  OF  BACTERIOLOGY  11 


activities  of  a  single  kind  of  organism  to  be  studied,  and 
its  power  for  the  good  or  ill  of  man  determined.  The  de- 
velopment, in  1882,  of  the  gelatine-plate  method  for  the 
separation  of  kinds  of  bacteria,  enabled  Koch  and  his  fol- 
lowers to  prove  the  bacterial  nature  of  the  cause  of  many 
of  the  most  important  diseases  of  man  and  the  lower  animals. 
Scarcely  a  year  has  passed,  since  1860,  that  has  not  been 
marked  by  discoveries  of  the  greatest  importance  to  human- 
ity in  bacteriology  and  its  related  sciences. 

Bacteriology  has  revolutionized  the  life  of  civilized  man. 
Without  it  our  great  cities  would  be  impossible,  for  they 
could  not  be  provisioned.  It  has  doubled  the  average  span 
of  human  life.  It  has  made  surgery  possible.  It  touches 
the  life  of  every  one  of  us  in  a  multitude  of  ways,  each  day, 
from  birth  to  death. 


CHAPTER  III 
THE    MORPHOLOGY  OF  MICROORGANISMS 

The  cell. — The  unit  of  life  is  the  cell,  which  consists  of  a 
limiting  membrane  inclosing  semi-liquid  contents.  Within 
the  cell  are  carried  on  all  of  the  activities  of  the  organism : 
herein  the  food  is  assimilated,  by-products  are  formed,  and 
energy  is  liberated  for  all  of  the  vital  processes. 

The  higher  plants  and  animals  are  constructed  out  of 
great  numbers  of  these  unit  cells,  which,  however,  are  col- 
lected into  groups  that  are  so  related  to  each  other  as  to 
form  tissues.  These  tissues  are  often  so  differentiated  in 
their  physiological  activity  that  they  may  perform  a  limited 
and  highly  specialized  function.  With  the  simpler  forms 
of  life,  such  as  the  bacteria,  all  of  the  complicated  chemical 
processes  essential  to  the  life  of  the  organism  take  place 
within  the  limits  of  a  single  cell.  Between  the  two  ex- 
tremes there  are  to  be  found  organisms  in  all  degrees  of 
complexity  as  to  structure  and  function.  The  types  that 
are  of  greatest  importance  in  the  decomposition  of  organic 
matter  are  either  unicellular  or  the  simpler  multicellular 
forms. 

With  the  multicellular  organisms,  variation  in  structure 
of  the  individual  is  limitless;  consequently,  morphology,  or 
the  science  that  describes  the  variation  in  form,  is  of  major 
importance.  The  simplicity  of  the  one-celled  plants,  the 
bacteria,  and  the  yeasts,  makes  a  description  of  their  mor- 
phology much  less  complex. 

The  division  of  life  into  plants  and  animals,  so  advanta- 
geous in  the  study  of  the  higher  forms,  is  not  especially  help- 

12 


MORPHOLOGY  OF  BACTERIA  13 

ful  when  the  lower  forms  are  under  consideration.  The  or- 
g^anisms  most  important  in  decomposition  processes  are 
morpholog:icalIy  more  closel}'  related  to  the  plants  than  to 
the  animals;  physiologically,  they  are  more  directly  allied 
to  the  animals.  It  is  customary,  however,  to  consider  the 
bacteria,  yeasts,  and  molds  as  members  of  the  plant  king- 
dom. 

Morphology  of  bacteria. — The  bacteria  may  be  defined 
as  unicellular  plants,  devoid  of  chlorophyl,  and  reproduc- 
ing by  division  of  the  cell  into  two  daughter  cells.  This 
mode  of  reproduction  has  given  to  them  the  name  of  schiz- 
omyceteSy  or  splitting  fungi. 

The  lower  or  the  true  bacteria  occur  in  three  form  types : 
spheres,  rods,  and  spirals.  A  spherical  organism  is  termed 
a  coccus  (plural,  cocci)  ;  a  rod  is  designated  as  a  bacillus 
(plural,  hacilli)  ;  a  spiral  organism  is  called  a  spirillum 

Q 

Fig.  1.     Forms  of  Bacteria 

A  spherical  organism  is  termed  a  coccus;  a  rod-shaped  one  a  bacillus;  a  spiral 
cell  is  called  a  spirillum 

(plural,  spirilla).  The  spheres  can  vary  only  in  size;  the 
rods  may  vary  in  the  ratio  of  the  two  axes,  being  either 
long  and  slender,  or  short  and  plump.  If  the  two  axes 
are  of  almost  equal  length,  the  rod  will  approach  a  sphere 
in  appearance.  Confusion,  therefore,  may  develop  in  such 
cases;  as,  for  instance,  in  the  lactic-acid  organism,  which 
is  so  short  a  rod  as  to  be  called  a  coccus  type  by  some  writ- 
ers. The  ends  of  the  rods  may  vary,  being  rounded  or 
square  cut,  or  even  in  a  few  instances  concave.  The  spiral 
types  may  present  all  the  variations  of  the  rods,  and  may 
vary  in  the  extent  to  which  the  cell  is  bei^t.     The  Qur- 


14 


AGRICULTURAL  BACTERIOLOGY 


vature  may  be  very  slight,  or  it  may  be  a  true  spiral.     The 

rigidity  of  the  bacterial 
cell  is  well  illustrated  in 
the  spiral  forms.  It  is 
evident  that  there  may 
be  a  gradual  gradation 
in  form  from  the  round- 
ed coccus  type  through 
to  the  spirilla. 

Frequently  under  the 
conditions  of  growth  in 
the  laboratory  and  less 
frequently  in  nature, 
cells  of  abliormal  shapes 
are  noted,  known  as  in- 
volution   forms.     It    is 


Fig.  2.     Cocci 
A.    spherical    organism    in    which    the    cells 
occur  in   irregular  shaped   masses   is   called 
staphylococcus 


After  Giinther. 


commonly  believed  that  these  cells  are  degenerate  forms 
and  are  not  capable  of 
reproduction.  The  de- 
viation from  normal  cell 
type  is  probably  occa- 
sioned by  growth  under 
unfavorable  conditions. 

Reproduction.  —  The 
bac^terial  cell  divides 
into  two  daughter  cells 
by  an  infolding  of  the 
protoplasm  in  the  mid- 
dle of  the  cell  until  the 
protoplasm  is  completely 
divided.  The  cell  wall 
is  then  formed,  and  fin- 
ally splits,  forming  the 
opposing  ends  of  the  new  cells 


Fig.  3.     Large  Bacilli 

A    rod-shaped   organism   in    which   the   cells 
occur  in  chains  is  called  a  streptobacillus 
After  Giinther. 


In  the  case  of  bacilli  and 


MORPHOLOGY  OF  BACTERIA 


15 


Fig.  4. 


Small  Bacilli 

After  Giinther. 


spirilla,  the  division  is  always  at  right  angles  to  the  long 

axis.     With    the    cocci, 

the    plane    of    division 

may  have  any  direction, 

since  all  axes  are  equal. 
Cell    reproduction    in 

the  multicellular   forms 

of  life  results  in  an  in- 
crease in  the  size  of  the 

individual;   in  the  uni- 
cellular forms  it  results 

in  multiplication  of  the 

number   off   individuals. 

Immediately    after    cell 

division,    the    daughter 

cells  are  much   smaller 

than  the  original  mother  cell  at  the  time  division  began. 

They  increase  rapidly 
in  size;  to  this  process 
the  term  growth  can 
be  applied.  Commonly 
one  speaks  of  the  growth 
of  bacteria  when  repro- 
duction is  referred  to. 

The  generation  period^ 
in  the  case  of  bacteria, 
is  the  time  required  for 
a  mature  cell  to  divide 
and  for  the  resulting 
cells  to  reach  maturity. 
With  many  forms  of 
bacteria  it  requires  only 
a    short    time    for    the 

process  of  division  to  be  completed;  in  some  instances  it 


Fig.  5.     SjDirilla 
The  organism   causing   Asiatic   cholera,  fre- 
quently   called    the    comma    bacillus 
After  Giinther. 


16 


AGRICULTUKAL  BACTERIOLOGY 


has  been  found  to  occur  in  twenty  minutes.     Such  a  rapid 

rate  is  attained  only  un- 
der the  most  favorable 
conditions  of  food  and 
temperature. 

This  cell  division  is 
termed  vegetative  repro- 
diwtio7i,  in  contrast  to 
a  second  method  that  is 
found  in  a  small  number 
of  the  bacteria,  viz.,  re- 
production by  the  for- 
mation of  spares.  In 
this  process  a  portion  of 
the  protoplasm  is  con- 
densed in  one  part  of 
the  cell  to  form  a  small 


Fig.  6.     Spirilla 

The  organism  causing  recurrent  fever.     The 
cells    show   many   turns    instead    of    only    a 
portion  of  a  turn  as  in  the  cholera  organism 
After  Giinther. 


spherical  or  oval,  highly  refractile  body,  to  which  the  term 


Fig.  7.     Spores 

A  portion  of  the  content  of  the  cell  is  condensed  into  a  body  which  appears  very 

bright  under  the  microscope.     On  germination  a  rod   similar  to  the  one  that 

produced   the    spore   results 

endospore  is  applied.     The  production  of  the  spore  is  fol- 
lowed by  the  death  of  the  cell  and  its  dissolution,  so  that  the 


MORPHOLOGY  OF  BACTERIA 


17 


spore  is  ultimately  set  free.  Spore  formation  is  virtually 
limited  to  a  few  of  the  bacilli,  and  does  not  occur  as  Ion":  as 
nutritive  conditions  admit  of  vegetative  reproduction.  It 
is  stimulated  by  lack  of  food  or  by  the  acciunulatioli  of  by- 
products of  cell  activit3\  Unfavorable  temperature  condi- 
tions for  growth  tend  to  prevent  the  formation  of  spores. 
It  is  a  specialized  function  of  the  organism,  and,  like  most 
such  functions,  occurs  within  a  narrower  range  of  condi- 
tions than  does  reproduction. 

The  diameter  of  the  spore  in  some  species  is  greater  than 
that  of  the  cell  it.self,  thus  producing  a  distortion  of  the 
cell.  In  the  case  of  B.  tetani,  the  organism  causing  lock- 
jaw, the  enlarged  spore 
is  at  the  end  of  the  cell 
forming  a  drumstick,  in 
which  case  it  is  called 
capitate.  If  the  spore 
is  centrally  located,  giv- 
ing to  the  cell  a  spin- 
dle-like appearance,  it 
is  called  a  Clostridium 
type.  The  spores  are 
readily  differentiated 
from  the  cell  proper  by 
their  higher  refractile 
power,  which  gives  them 
the  appearance  of  bright 
dots  under  the  micro- 
scope. In  stained  preparations  they  still  appear  as  bright, 
unstained  spots  in  the  stained  ciells,  since  they  do  not  t?jke 
the  stain  in  the  ordinary  methods  of  treatment. 

The  bacterial  spores  possess  greater  powers  of  resistance 
to  various  physical  and  chemical  agents  than  any  other 
form  of  life.     They  are  especially  resistant  to  heat.     Some 


Fig.  8.     Spores 
The  unstained  body  to  be  noted  in  most  ^ of 
the  cells  is  a  spore  formed  by  the  condensa- 
tion  of   a   portion    of   the   cell   content 
After  Giinther. 


18 


AGRICULTURAL  BACTERIOLOGY 


spores  will  withstand  the  temperature  of  boiling  water  for 
sixteen  hours.  They  have  been  found  alive  on  dried  her- 
barium specimens  after  ninety-two  years,  and  in  the  au- 
thor's laboratory  the  spores  of  Bad.  anthracis  remained 
alive  in  water  for  seventeen  years.  They  are  also  resistant 
to  chemicals.  They  assume  an  important  function  in  the 
preservation  of  food  and  in  the  prevention  of  diseases,  since 
their  destruction  is  often  a  matter  of  great  difficulty. 

The  spore,  placed  in  a  favorable  environment,  germinates 
and  produces  a  cell  similar  to  the  one  that  formed  the 
spore.  Since  a  cell  produces  but  a  single  spore,  spore 
formation  is.  not  a  matter  of  growth,  but  of  reproduction. 
The  germination  may  result  in  the  rupture  of  the  spore  at 
the  end,  and  the  young  cell  emerges  with  its  long  axis  par- 
allel to  that  of  the  spore.  In  other  types  the  cell  may 
emerge  at  the  side  of  the  spore.  In  some  instances  the  spore 
swells  and  the  spore  wall  is  absorbed  in  the  cell  substance. 
The  tj^pe  of  spore  germination  may  enable  the  differentia- 
tion of  closely  related  morphological  forms  to  be  made. 

Cell  aggregates. — The  arrangement  of  the  cells  fre- 
quently makes  possible  the  recognition  of  species  among 


Fig.  9.     Arrangement  of  Cocci 
Streptococci,   Sarcinae,   Staphylococci 

the  higher  plants  and  animals.  Something  of  similar  na- 
ture can  be  used  in  the  study  of  bacteria.  After  cell  divi- 
sion has  occurred,  the  daughter  cells  may  separate  at  once, 
or  the  cells  may  cohere  for  a  time.     If  the  cohering  cells 


MORPHOLOGY  OF  BACTERIA 


19 


continue  to  reproduce 
may  consist  of  a  few 
cells  or  of  many.  If 
the  orp:anism  is  a  coc- 
cus, the  term  strepto- 
coccus (chain  coccus) 
is  applied:  if  a  bacil- 
lus, streptohacUlus  is 
used. 

In  the  case  of  the 
bacilli  this  is  the  only 
cell  aorgregrate  with 
rejrularity  of  form 
that  can  occur.  It  is 
probable  that  the 
cells  in  a  chain  are  in- 
closed in  a  common 
sheath.     Various    other   forms 


a  chain  of  cells  will  result,  which 


Fig.   10.     A  St  Kptococcus 

One  of  the  organisms  concerned  in  the  souring 

of  milk 

After  Orla  Jensen. 


of  aggregates  are  found 
among  the  cocci.  If 
the  plalies  of  division 
are  always  parallel  and 
the  cells  cohere,  a  chain 
results,  as  noted  above. 
If  the  tendency  is  for 
but  two  cells  to  cohere, 
the  term  diptococcus  is 
used.  If  the  planes  of 
division  have  no  definite 
direction,  the  progeny 
of  a  single  cell  will  form 
an  irregular  cell  mass. 
Such  an  organism  is 
called  a  staphylococcus^ 
from  its  similarity  to  a  bunch  of  grapes.     Cocci  may  occur 


Fig.   11.     liact.  Anthracis 

Threads    consisting    of    many    cells    charac 

terize  this  organism 

After  Giinther. 


20 


AGRICULTURAL  BACTERIOLOGY 


in  bunches  of  fours.  Such  grouping  is  called  a  tetracoccus. 
Again,  the  successive  planes  of  division  may  be  in  three 
dimensions  of  space,  resulting  in  packets  of  cells,  to  which 
the  name  sarcina  is  applied. 

The  spirilla  exhibit  the  same  cell  grouping  as  do  the  ba- 
cilli, although,  as  a  rule,  it  is  less  pronounced. 

Cell  structure. — The  bacterial  cell  wall  is  a  relatively 
firm  membrane,  through  which  all  food  must  pass  by  dif- 
fusion. Lining  the 
cell  wall  is  a  layer  of 
protoplasm,  the  ecto- 
plast,  which  has  a  se- 
lective action  on  sub- 
stances in  solution  in 
the  cell  sap,  or  in  the 
liquid  in  which  the 
cell  occurs.  Since 
the  action  of  this  cell 
structure  determines 
what  substances  en- 
ter or  leave  the  cell. 
Fig.  12.     A  Tetracoccus  it  is  one  of  the  most 

It  will  be  noted  that  the  cells  tend  to  occur  in        imDOrtaut         elements 
aggregates  of  four  . 

After  Orla-Jensen.  of     the     CCll.       If     the 

cells  are  placed  in  a  strong  sugar  or  salt  solution,  the  proto- 
plasm shrinks  and  the  cell  is  said  to  be  plasmolyzed,  a  con- 
dition in  which  growth  is  impossible. 

The  nucleus  of  the  cell  of  the  higher  plant  and  animal 
is  a  structure  of  the  utmost  importance,  since  it  governs 
for  the  most  part  the  physiological  activities  of  the  cell.  It 
plays  the  most  important  role  in  cell  division.  Its  impor- 
tance is  such,  in  the  cells  of  the  higher  forms,  that  it  would 
seem  impossible  for  any  ceil  to  function  without  a  nucleus. 
A  definite  nucleus  is  not  found  in  the  typical  bacterial  cell. 


MORPHOLOGY  OF  BACTERIA 


21 


From  the  relation  of  cells  to  stains,  the  conclusion  has  been 
drawn  that  the  substance  of  the  bacterial  cell  is  essentially 
nuclear  in  character. 

Inclusions  of  various  kinds  are  sometimes  to  be  observed 
in  the  bacteria.  These  bodies,  termed  metachromatic 
granules,  may  react  to  the  stains  in  such  a  way  as  to  dif- 
ferentiate them  from  the  rest  of  the  cell  contents.  Granules 
of  j?lycoo:en  and  of  sulphur  are  found  in  some  species,  as  are 
also  droplets  of  oil. 

The  outer  layer  of  the  cell  wall  is  often  of  a  gelatinous 
nature  and  more  or 
less  tliickened,  form- 
m<x  what  is  known  as 
the  capsule.  It  is 
probable  that  the 
presence  of  some  of 
the  capsulated  bac- 
teria causes  the  solu- 
tions in  which  they 
are  growinof  to  be- 
come ropy  or  slimy 
as  is  the  case  with 
ropy  bread  and  slimy 
milk.  Some  bacteria 
are  embedded  in  a 
of     gelatinous 


mass 


Fifj.  13.     Capsules 
Each  cell  is  surrounded  by  a  gelatinous  layer, 
which  appears   as   a  clear  space  in  the  photo- 
graph After  OrlaJensen. 

material  secreted  by  the  cells,  in  which  case  the  mass  of  or- 
ganisms is  termed  a  zoiigloea.  The  mass  may  be  so  firm  as 
to  have  a  leathery  nature. 

Motility. — Many  species  of  bacteria  have  the  power  of  in- 
dependent motion  when  they  are  in  a  suitable  liquid.  The 
organs  of  locomotion  are  delicate  whiplike  appendages  var- 
iously distributed  on  the  cell.  The  term  flagella  (singular 
flageJhim)  is  applied  to  them.     A  monotrichous  cell  is  pro- 


22  AGRICULTURAL  BACTERIOLOGY 

vided  with  a  single  flagellum  at  one  end.  If  two  or  more 
flagella  are  present  at  one  end,  the  term  lophotrichous  is 
used.  When  clusters  of  flagella  are  at  either  end, 
amphitrichous  is  applied.  And  when  the  flagella  are 
distributed  over  the  entire  cell,  it  is  known  as  pcritri- 
chous. 

The  flagella  are  exceedingly  delicate,  and  are  so  small 
that  they  are  not  visible  in  ordinarj^  microscopic  prepara- 
tions. To  make  them  apparent,  the  preparation  is  treated 
in  such  a  way  as  to  precipitate  something  upon  them,  thus 
increasing  their  apparent  diameter.  These  locomotor  ap- 
pendages, which  are  usually  much  longer  than  the  cell  itself, 
are  not  found  on  the  cocci.  Many  of  the  bacilli  and  nearly 
all  of  the  spirilla  are  motile. 

The  space  that  can  be  traversed  by  even  the  most  ac- 
tively motile  cell  is  small,  probably  not  more  than  an  inch 
or  two  in  an  hour.  In  comparison  to  their  size  the  motion 
is  quite  rapid.  Some  have  been  shown  to  travel  twenty 
times  their  own  length  in  one  second,  a  relatively  much 
faster  rate  than  that  of  a  speeding  race-horse.  Some  of 
the  motile  spirilla  can  reverse  their  direction  without  the 
turning  about  of  the  cell.  In  others,  the  cell  must  turn 
to  reverse  the  direction  of  movement.  It  should  be  remem- 
bered that  in  the  case  of  the  peritrichous  forms  there  must 
be  coordination  of  movement  among  all  of  the  flagella  of  a 
single  cell.  These  arrangements  give  some  idea  of  the  com- 
plexity of  the  bacterial  cell. 

Size  of  bacteria. — The  unit  of  measurement  in  micros- 
copy is  the  micron,  which  is  one  thousandth  of  a  milli- 
meter, or  approximately  one  twenty-five  thousandth  of  an 
inch.  It  is  usually  expressed  by  the  Greek  letter  /x.  The 
great  majority  of  the  bacteria  are  from  0.5  to  5  microns  in 
length  or  diameter. 

It  is  difficult  to  obtain  any  appreciation  of  the  minute- 


MORPHOLOGY  OF  BACTERIA  23 

ness  of  the  bacteria.  If  they  are  represented  by  tiny  cubes, 
a  micron  on  each  edge,  one  billion  of  them  would  be  con- 
tained in  a  cubic  millimeter,  and  one  thousand  billion  in  a 
cubic  centimeter.  If  a  sample  of  milk  contains  a  billion 
bacteria  per  cubic  centimeter,  it  means  that  less  than  one 
thousandth  of  its  volume  consists  of  bacteria. 

Ultramicroscopic  organisms. — It  is  known  that  there  are 
forms  of  life  so  small  that  they  are  invisible  under  the 
highest  powers  of  the  microscope.  An  object  having  a  di- 
mension less  than  0.2  micron  can  not  be  demonstrated  by 
the  microscope.  The  term  ultramicroscopic  organism  is 
applied  to  such.  The  proof  of  their  existence  lies  in  the 
fact  that  an  animal  can  be  inoculated  with  a  minute  quan- 
tity of  the  blood  of  another  animal  suffering  from  some 
one  of  certain  diseases.  The  presence  of  organisms  in  the 
blood  injected  can  not  be  demonstrated  microscopically. 
The  inoculated  animal  acquires  the  disease.  From  it 
another  animal  can  be  inoculated.  The  process  can  be 
extended  through  as  long  a  series  as  is  desired,  with  con- 
stant results,  which  can  be  explained  only  by  the  presence 
of  a  living  organism  in  the  original  material  used.  Only 
a  living  form  could  thus  perpetuate  itself.  The  term 
filterable  virus  is  also  applied  to  such  minute  organisms, 
for  the  reason  that  they  pass  through  filters  that  remove 
the  bacteria. 

One  gains  some  conception  of  the  size  of  atoms  and  mole- 
cules when  it  is  recognized  that  in  each  of  these  minute 
organisms  there  are  many  different  chemical  substances, 
and  many  molecules  of  each.  Chemical  processes  and  trans- 
formation of  energy,  that  man  can  not  and  probably  never 
will  be  able  to  duplicate,  since  they  represent  the  life  pro- 
cess, the  power  of  self-perpetuation,  are  going  on  in  each 
minute  cell. 

Higher  bacteria, — Between  the  various  typical  groups 


24  AGRICULTURAL  BACTERI0L0(;Y 

of  life,  one  finds  transition  forms  that  have  the  character- 
istics of  both  of  the  related  groups  to  a  greater  or  less 
degree.  Such  forms  occur  between  the  true  bacteria  and 
the  true  molds,  or,  more  properly  speaking,  the  filamentous 
fungi.  The  term  higher  bacteria,  or  trichohacteria,  is  ap- 
plied to  these  in  opposition  to  the  haplohacteria,  or  strictly 
unicellular  forms. 

The  higher  bacteria  occur  in  threads  or  filaments.  A 
number  of  cells  are  contained  in  a  common  sheath.  It  is 
probable  that  the  individual  cells  are  capable  of  indepen- 
dent existence.  Since  they  occur  in  filaments,  they  give 
evidence  of  a  certain  differentiation  in  function.  Some  of 
the  cells  are  concerned  with  reproduction,  others  with  the 
anchoring  of  the  thread  to  its  substratum.  In  such  organ- 
isms is  found  the  beginning  of  the  division  of  labor,  the  dis- 
tinguishing characteristic  of  the  higher  forms  of  life.  The 
filaments  are  usually  unbranched.  Some,  however,  show 
true  branching,  a  property  that  allies  them  to  the  molds. 
Still  others  have  false  branching,  due  to  the  misplacement 
of  a  cell  in  the  threa-d.  A  cell  forced  out  of  its  position  in 
the  chain  by  its  division  gives  rise  to  a  new  thread. 

Another  property  that  allies  the  higher  bacteria  to  the 
molds  is  the  production  of  spores,  or  conidia,  by  the  divi- 
sion in  the  three  dimensions  of  space  of  the  upper  cells  of 
he  sessile  thread.  The  conidia  are  motile  in  some  instances ; 
in  others,  non-motile.  They  leave  the  sheath  in  which  they 
have  been  formed,  and  float  away  to  establish  new  threads 
vhen  they  lodge  on  a  favorable  substratum.  The  spores  may 
germinate  while  still  in  the  sheath,  giving  rise  to  a  whorl 
of  threads. 

Among  the  higher  bacteria  are  to  be  found  some  of  great 
practical  importance,  such  as  the  iron  bacteria,  which  fre- 
quently cause  the  clogging  of  water-mains  and  drains ;  and 


MORPHOLOGY  OF  BACTERIA  25 

certain  disease-producing  organisms,  as  the  one  causing 
lumpy  jaw  in  cattle. 

Classification  of  bacteria. — Many  attempts  have  been 
made  to  erect  a  classification  of  bacteria  comparable  to  the 
classifications  used  in  botany  and  zoology-.  The  latter  are 
based  on  morphology-.  Due  to  the  simple  morphology  of 
the  bacteria,  a  classification  based  thereon  is  unsatisfactory 
and  of  limited  value.  For  purposes  of  identification,  not 
only  must  morphology  be  considered,  but  also  the  action  of 
the  organism  on  the  food  material,  the  physiology  of  the 
organism,  and  the  appearance  of  the  masses  of  cells  as  they 
occur  in  the  artificial  cultures  of  the  bacteriologist,  i.  e.  the 
cultural  characteristics. 

The  classification  that  is  in  most  common  use  is  that  of 
Migula.  It  is  as  complete  as  possible  where  classification  is 
based  on  morphology  alone.  As  modified  by  Buchanan 
and  presented  in  simple  form,  it  is  as  follows : 

MIGULA'S  CLASSIFICATION  Of  THE  EUBACTERIA 

(Modified) 

{Forms  of  economic  importance  only) 

Suborder  T.     H aplohacteria.     Bacterial  cells  not  permanently  united 

into  filaments,  without  sheaths. 

Family  I.     Coccacew.     Cells  spherical,  at  least  when  free. 

1.  Cells  non-motile: 

a.  Cell  division  in  one  plane,  cells  frequently  remaining  at- 
tached   in   chains. . Streptocnccus 

h.  Cell  division  in  two  planes  (sometimes  irregular),  re- 
sulting in  formation  of  flat  plates  or  of  masses  of 
cells    Micrococcus 

c.  Cell  division  in  three  planes,  all  at  right  angles,  4,he  cells 
remaining  unided  after  division,  forming  cubes  or 
packets    Sarcina 

2.  Cells  motile: 

a.  Same  as  Micrococcus,  but  with  flagella Planococcua 

h.  Same  as  Sarcina,  but  with  flagella Planosarcina 

Family  II.     Bacteriacece.     Cells  cylindrical  in  shape,  not  bent. 
1.  Cells  non-motile    Bacterium 


26  AGRICULTURAL  BACTERIOLOGY 

2.  Cells  motile: 

a.  With  polar  flagella   Pseudomonas 

b.  With  peritricliouH  (hi<i;ella  Bacillus 

Family  III.     Spirillacew.     Cells  elongated  and  bent,  usually  spirals 

or  segments  of  spirals. 

1.  Cells  non-motile Spirosoma 

2.  Cells  motile : 

a.  Cells     short,     comma-shaped,     one     to     three     polar     fla- 
gella     • Microspira 

6.  Cells  longer,  with  tuft  of  polar  flagella Spirillum 

c.  Cells   very   long  and   slender,   flexible.     Flagella,   if  pres- 

ent, demonstrated  only  with  difficulty SpirochcBta 

Suborder    II.     Trichobacteria.      (Family Chla'mydohacteriacecB) 

Cells  cylindrical,  united  in  threads  or  filaments,  surrounded 
by  a  sheath. 

a.  Filaments    un'branchod    Leptothrix 

&.  Filaments  showing  false  branching   Cladothrix 

c.  Filaments  showing  true  branching: 

1.  Spores  produced    Nocardia 

2.  No  spores  observed  Actinomyces 

The  terms  applied  to  specific  organisms  have  various 
meanings.  Usually  they  refer  to  the  type  of  decomposi- 
tion caused  by  the  organism,  the  disease  produced  by  it, 
its  habitat,  or  its  respective  group  morphologically  Ex- 
amples are  as  follows:  Bad.  lactis  acidi,  a  non-motile  rod 
that  produces  lactic  acid  as  its  chief  by-product ;  B.  typho- 
sus, a  motile  rod  causing  typhoid  fever ;  B.  coli  communis,  a 
motile  rod  the  habitat  of  which  is  that  part  of  the  digestive 
tract  known  as  the  colon;  B.  Welchii,  a  motile  rod  named 
from  its  discoverer,  Dr.  William  Welch,  one  of  the  most 
prominent  of  Ameriican  bacteriologists. 

The  subjects  of  classification  and  nomenclature  in  bacter- 
iology are  much  confused.  The  same  organism  may  be 
described  and  referred  to  in  the  literature  under  many 
names. 

Morphology  of  yeasts. — The  yeasts,  or  saccharomycetes, 
as  they  are  freqently  called  because  of  their  growth  in  sugar 
solutions,  are  unicellular  organisms  like  the  true  bacteria, 


MORPHOLOGY  OF  BACTERIA 


27 


but  they  are  more  complex  in  structure,  possessing  a  def- 
inite nucleus  which  is  small,  and  recognizable  with  difficulty, 
if  at  all,  in  unstained  preparations.  It  can,  however,  be 
demonstrated  by  proper  methods  of  staining.  The  proto- 
plasm contains  granules,  oil  globules,  and  vacuoles  that  are 


14.     Yeasts 

The  cells   reproduce  by   budding.     The   large  clear  areas   in  some  of  the  cells 
are   vacuoles,    which    are    filled    with    cell   sap 

filled  with  cell  sap.     The  wall  of  the  yeast  cell  is  a  rela- 
tively firm  structure  of  yeast  cellulose. 

The  yeast  cell  may  be  oval,  ellipsoidal,  or  cylindrical, 
rarely  spherical.  The  shape  is  not  so  constant  in  form  for 
a  given  species  as  is  the  case  with  the  bacteria.  The  yeasts 
are,  as  a  rule,  larger  than  the  bacteria,  the  cells  commonly 
ranging  from  2.5  to  12  microns  in  width.  The  grouping 
shows  little  of  the  regularity  that  is  noted  among  some  of 
the  bacteria.  Reproduction  is  accomplished  by  the  vegeta- 
tive method,  or  by  the  production  of  spores.  The  former 
takes  place  by  the  formation  of  buds  on  any  portion  of  the 


28      AGRICULTURAL  BACTERIOLOGY 

cell.  A  portion  of  the  nucleus  passes  into  the  minute  pro- 
tuberance, which  then  enlarges,  and  is  separated  from  the 
mother  cell  by  a  constriction.  The  daughter  cell  may  re- 
main attached,  or  may  separate  at  once  from  the  mother 
cell. 

Spore  production  in  the  case  of  the  true  yeasts  is  a  method 
of  increase  in  numbers,  since,  as  a  rule,  more  than  one 
spore  is  produced,  from  two  to  eight  being  usual.  The 
spores  are  often  termed  ascospores,  and  the  spore-producing 
cell  an  ascus.  The  spores  are  not  normally  produced  in 
growing  cultures.  They  have  various  shapes  and  markings. 
In  one  species,  Saccharomycetes  anomalus,  they  are  shaped 
like  a  derby  hat.  The  ascopores  germinate  by  swelling, 
bursting  the  wall,  and  budding.  The  true  yeasts  are  those 
that  reproduce  by  budding  and  spores.  The  false  yeasts 
do  not  produce  spores.  The  term  torulce  is  often  applied  to 
the  latter. 

The  yeast  spores  are  not  so  resistant  to  heat  as  are  the 
bacterial  spores ;  indeed  they  are  but  little,  if  any,  more  re- 
sistant than  the  vegetative  cell.  The  non-resistance  of  the 
yeast  spore  to  heat  is  of  great  importance  in  food  preserva- 
tion. 

Molds. — The  molds  represent  a  more  highly  developed 
and  more  complex  group  of  organisms  than  do  the  bacteria 
and  yeasts.  Many  hundred  genera  are  known.  It  is  possi- 
ble to  give  only  a  few  of  the  more  important  points  of  their 
morphology,  especially  of  those  that  are  of  practical  impor- 
tance. The  molds  are  multicellular,  and  exhibit  a  division 
of  work  among  the  cells.  Some  are  concerned  with  nutri- 
tive procei?ses,  others  with  reproduction. 

The  mold  plant  consists  of  a  network  of  branching 
threads,  called  hyphw.  The  threads  are  formed  by  cylindri- 
cal cells  placed  end  to  end.  The  threads  concerned  with  nu- 
trition are  termed  vegetative  hyphce;  those  concerned  with 


MORPHOLOGY  OF  MOLDS  29 

reproduction,  fertile  hypJice.  The  term  mycelium  is  ap- 
plied to  the  entire  mass  of  growth  resulting  from  a  single 
spore. 

The  filaments  may  be  divided  by  cross-walls,  or  septa,  or 
they  may  not  be  so  divided.  In  the  septate  mycelium  each 
cell  contains  a  nucleus.  In  the  non-septate  mycelium,  nu- 
clei occur  at  intervals  along  the  thread  in  the  protoplasm. 
Therefore  even  the  non-septate  molds  are  to  be  classed  as 
multicellular.  The  threads  branch  at  frequent  intervals. 
The  microscopic  appearance  of  the  mycelium  is  that  of  a 
mass  of  tangled  filaments.  The  filaments  are  not  usually  all 
in  contact  with  the  food,  but  rise  into  the  air  to  some  extent, 
giving  to  the  typical  mold  a  fluffy  appearance.  The  hyphai 
are  usually  colorless. 

Reproduction  is  by  the  formation  of  spores,  which  are 
produced  in  enormous  numbers.  In  some  species  both 
S3xual  and  asexual  spores  are  produced.  The  former  are 
of  small  practical  importance  and  will  not  be  treated.  The 
asexual  spores  are  most  often  borne  on  hyphai  that  rise  into 
the  air  and  are  thus  out  of  contact  with  the  moist  food  ma- 
terial, a  fact  of  importance  when  their  distribution  is  con- 
sidered. The  manner  of  production,  their  size,  shape  and 
color,  are  the  most  important  characteristics  used  in  the 
classification  of  molds.  The  spores  are  often  colored, 
brown,  black,  and  green  being  the  most  common. 

In  a  number  of  the  more  important  groups  of  molds,  the 
spores  are  produced  on  the  ends  of  the  filaments.  Such  fil- 
aments are  called  conidiophores,  and  the  spores  conidia.  In 
others  they  arc  formed  in  closed  sacs,  called  sporangia,  the 
filament  bearing  the  sac  being  termed  a  sporangiaphore. 
The  latter  type  of  spore  formation  is  limited  to  the  non- 
septate  molds.  The  mature  sporangium  usually  bursts, 
and  the  numerous  sporangia  spores  are  set  free.  The  spor- 
mgium  is  quite  comparable  to  the  ordinary  puff-ball.     Some 


30 


AGRICULTURAL  BACTERIOLOGY 


oc|i? 


Fig. 


Spore-formation  by  Molds 


The   manner   of    spore-formation    by    the    aspergillus    molds,    upper    left,    by   the 
penicillium   molds,    right,   and   by   the   mucor   molds,    lower  left 

of  the  molds  form,  spores  by  the  breaking  up  of  entire  fila- 
ments into  short  segments.  Such  spores  are  called  o'idia. 
Oidimn  lactis,  the  mold  that  develops  on  milk,  is  the  most 
important  from  a  practical  standpoint. 

The  most  common  molds  appearing  in  foods  are  the 
mucors,  the  penicillia,  and  the  aspergilli.  The  former  pro- 
duce the  spores  in  sacs.  The  most  common  is  Rhizopiis 
nigricans  producing  the  soft  rot  on  vegetables  like  sweet 
potatoes.     The  spores  are  black,  and  at  the  point  at  which 


MORPHOLOGY  OF  MOLDS  31 

the  fertile  hyplije  branch  from  the  vegetative  hyphae  clus- 
ters of  rootlike  hold-fasts  or  rhizoids  are  produced. 

In  the  genus  Aspergillus  the  spores  are  borne  on  the  ends 
of  club-shaped  stalks,  called  steriymata  (singular,  ster- 
igma),  which  are  grouped  on  the  enlarged  end  of  the  con- 
idiophore.  The  spores  are  green,  yellow,  orange,  brown,  or 
black.  Aspergillus  niger  is  the  most  common  of  the  black- 
spored  types;  Aspergillus  glaucus,  which  occurs  on  grain, 
silage,  canned  fruits  and  vegetables,  is  the  most  common 
green-spored  one. 

In  the  case  of  the  penicillia,  the  conidiophore  branches 
one  or  more  times,  producing  a  cluster  of  parallel  hyphae, 
from  the  end  of  which  a  chain  of  conidia  is  abstracted. 
This  results  in  a  broom-  or  brush-like  appearance,  which 
gives  the  genus  its  name  of  Penicillium,  from  the  Latin  word 
for  brush.  The  most  conunon  members  of  the  group  have 
green  spores. 

The  mold  spores,  like  those  of  the  yeasts,  are  easily  killed 
by  moist  heat. 

In  the  case  of  the  bacteria  and  yeasts,  true  unicellular 
organisms,  it  is  necessary  for  each  cell  to  be  in  direct  contact 
with  the  food.  In  the  case  of  a  mass  of  cells  growing  on  a 
solid,  the  nutrients  may  pass  by  diffusion  through  the  mass 
of  cells  not  in  direct  contact  with  the  medium.  In  the  case 
of  the  molds,  cells  in  actual  contact  with  the  food  may 
pass  the  same  to  other  cells  not  in  contact  with  it.  This 
enables  the  molds -to  invade  vessels  that  are  absolutely  pro- 
tected from  the  bacterial  invasion,  such  as  the  cultures  of 
the  bacteriologist. 

The  production  of  spores  in  the  air,  and  thus  out  of  con- 
tact with  a  moist  substratum,  enables  the  spores  to  be  easily 
carried  away  from  their  point  of  production  by  air  cur- 
rents. This  method  of  transportation  is  favored  by  their 
lightness.     Their  ubiquitous  distribution  on  every  object  is 


32  AGRICULTURAL  BACTERIOLOGY 

the  result  of  the  profuseness  with  which  they  are  produced 
and  the  ease  with  which  they  are  distributed. 

Protozoa. — This  term  is  applied  to  unicellular  animals, 
some  of  which  are  of  interest  to  us  because  of  their  relation 
to  bacteria,  and  because  some  of  them  produce  diseases  in 
man  and  in  domestic  animals  in  much  the  same  way  as  do 
the  bacteria. 

The  animal  cell  wall  lacks  the  rigidity  and  firmness  of 
the  plant  cell  wall.  For  this  reason,  the  protozoa  do  not 
have  the  definiteness  of  form  that  marks  the  unicellular  bac- 
teria and  yeasts. 

Many  of  the  protozoa  ingest  solid  food,  again  a  differentia- 
tion from  the  unicellular  plants.  Bacteria  serve  as  food  for 
some  of  the  protozoa  to  be  found  in  soil  and  water. 


CHAPTER  IV 

CULTIVATION  AND  STUDY  OF  BACTERIA, 
YEASTS,  AND  MOLDS 

The  studies  of  the  botanist  and  the  zoologist  are  more 
largely  confined  to  the  structure  of  the  individual  than  to 
its  physiology,  to  form  rather  than  to  function.  The  bac- 
teriologist finds  that  little  of  practical  importance  can  be 
gained  from  such  a  study  of  the  organisms  in  which  he  is 
interested.  He  must  extend  his  observations  to  the  part 
they  play  in  the  decomposition  of  organic  matter.  The 
bacteria,  the  yeasts,  and  the  molds  occur  in  nature  in  such 
confusion  and  in  such  mixture  of  kinds  that  a  study  of  them 
in  their  native  habitat  is  of  no  avail.  Before  one  can  learn 
anything  of  the  functional  activities  of  a  single  kind,  it 
must  be  separated  from  all  others,  and  it  "must  be  grown  un- 
der controlled  conditions.  This  work  involves  the  isolation 
and  the  cultivation  of  pure  cultures,  that  is,  those  that  con- 
tain but  a  single  kind  in  which  each  cell  is  like  every  other 
cell. 

Culture  media. — Almost  any  kind  of  organic  matter  will 
servers  food  for  some  tj^pe  of  organism.  Under  laboratory 
conditions  it  is  desirable  to  use  as  few  kinds  of  nutritive 
materials  as  possible,  and  to  have  these  supply  conditions  for 
the  growth  of  as  many  kinds  of  organisms  as  possible. 
These  nutritive  materials,  when  used  in  the  laboratory  for 
the  growth  and  cultivation  of  microorganisms,  are  called 
culture  media  (singular,  medium).  It  is  essential  that  all 
or  a  portion  of  the  material  used  be  soluble  in  water,  other- 
wise it  can  not  pass  through  the  cell  membrane  and  the 
layer  of  cytoplasm  lining  the  cell  wall.     It  is  essential  that 

33 


34  AGRICULTURAL  BACTERIOLOGY 

the.  chemical  reaction  be  favorable  for  the  organism  to  be 
grown. 

The  bacteriologist  has  succeeded  in  devising  what  may  be 
termed  basal  culture  media,  to  which  may.  be  added  amend- 
ments to  adapt  them  better  to  the  growth  of  specific  organ- 
isms. The  great  basal  culture  medium  is  broth  or  bouillon, 
prepared  by  infusing  one  part  of  chopped  lean  meat  (beef 
or  veal  most  commonly)  in  two  parts  of  water.  The  sol- 
uble constituents  are  extracted  from  the  meat.  The  insol- 
uble portion  is  filtered  off,  and  to  the  filtrate  is  added  1  or  2 
per  cent,  of  peptone.  The  latter  is  prepared  from  meat  or 
blood  by  digesting  it  with  one  of  the  agents  that  are  active 
in  the  intestinal  tract  of  animals  until  the  meat  or  blood  is 
changed  into  a  mixture  of  simpler  products  that  are  soluble 
in  water.  The  infusion  of  meat  to  which  peptone  has  been 
added  is  boiled  to  coagulate  the  albumens  present.  Its  re- 
action is  then  adjusted  to  the  desired  point  by  methods  that 
can  not  be  discussed  in  sufiicient  detail  to  warrant  their 
treatment  here. 

Acidity  and  alkalinity  are  due  to  the  presence  of  hydro- 
gen (H)  and  hydroxyl  ions  (OH)  respectively.  Any  solu- 
tion in  which  the  former  are  in  excess  will  be  acid  in  reac- 
tion. If  the  hydroxyl  ions  are  in  excess  of  the  hydrogen 
ions,  the  solution  will  be  alkaline.  If  both  are  present  in 
equal  numbers,  the  material  will  be  neutral  in  reaction. 
Pure  water  is  the  great  example  of  a  neutral  substance. 
For  most  microorganisms  the  nutrient  medium  should  be  ap- 
proximately neutral.  It  is  doubtful  whether  there  is  any 
microorganism  that  will  not  grow  in  a  neutral  reaction  when 
other  conditions  are  favorable. 

The  broth  is  filtered,  after  its  reaction  has  been  corrected, 
to  remove  all  coagulated  and  suspended  matter,  since  it  is 
desirable  to  have  the  medium  clear  in  order  that  the  growth 
of  bacteria  therein  can  be  more  easily  seen. 


CULTIVATION  OF  MICROORGANISMS         35 

Coiumercial  extract  of  beef  may  be  used  in  place  of  fresh 
meat,  and  is  widely  employed  on  account  of  its  convenience. 
Sugars  of  various  kinds,  glycerin,  and  other  substances  may 
l)e  added  to  the  broth  to  adapt  it  to  the  needs  of  specific 
organisms.  This  simple  culture  'medium  will  permit  the 
growth  of  the  great  majority  of  organisms  in  which  the 
bacteriologist  is  interested. 

Milk,  which  contains  a  mixture  of  sugars,  proteins,  and 
mineral  substances,  is  admirably  adapted  to  the  cultivation 
of  bacteria. 

Materials  that  are  naturally  solid  or  that  are  solidified 
l)y  heat  are  used  as  media.  Prominent  among  these  are 
slices  of  various  vegetables.  Potato  is  most  commonly  used, 
as  are  the  mixture  of  the  white  and  yolk  of  the  egg,  and 
blood  serum. 

Liquefiable  solid  media. — It  is  neces.sary  to  have  a  me- 
dium that  is  liquid  at  high  temperatures  and  that  becomes 
solid  on  cooling  for  purposes  of  isolation,  as  will  be  ex- 
plained later.  Such  a  medium  can  be  obtained  by  the  ad- 
dition of  10  per  cent,  of  gelatin  to  the  beef  broth.  This 
medium  will  remain  solid  up  to  77°  F.  Since  some  bacteria 
do  not  grow  at  such  low  temperatures,  gelatin  can  not  be 
used  for  their  cultivation.  Certain  bacteria  have  the  power 
of  digesting  or  liquefying  it,  an  advantage  or  a  disadvan- 
tage, depending  on  the  service  the  medium  is  to  yield. 

The  broth  may  also  be  made  into  a  liquefiable-solid  me- 
dium by  the  addition  of  from  1  to  1.5  per  cent,  of  agar,  a 
substance  obtained  from  certain  seaweeds  found  in  Japan 
and  China.  The  medium  to  which  the  agar  is  added  ex- 
hibits the  peculiar  property  of  melting  at  98°  C.  (208°  F.), 
but  of  not  solidifying  until  it  is  cooled  to  38°  C.  (100°  F.). 
This  enables  the  bacteria  to  be  mixed  with  it  while  it  is  at 
a  temperature  that  will  not  injure  them,  and  for  the  cul- 
tures to  be  kept  at  any  desired  temperature  without  becom- 


36  AGRICULTURAL  BACTERIOLOGY 

ing  liquid.  The  agar  is  not  liquefied  by  any  of  the  ordi- 
nary bacteria;  it  serves  simply  as  a  solidifying  material, 
while  gelatin  may  serve  as  food  for  many  bacteria.  Gelatin 
is  a  protein ;  agar,  a  carbohydrate. 

The  introduction  of  gelatin  in  1882,  by  Robert  Koch, 
made  possible  the  great  developments  in  bacteriology  that 
took  place  in  the  last  two  decades  of  the  nineteenth  century. 

Sterilization  of  culture  media. — The  media  as  prepared 
will  contain  many  microorganisms  that  were  in  the  ingredi- 
ents or  the  vessels  used.  These  organisms  must  be  de- 
stroyed if  the  media  are  to  be  of  any  value.  This  is  most 
commonly  accomplished  by  heating  the  media  until  they 
are  free  from  living  forms.  They  are  then  said  to  be 
sterile.  The  process  is  termed  sterilization.  The  media 
ordinarily  will  contain  bacteria,  yeasts,  and  molds,  and  the 
spores  of  each.  A  short  exposure  to  the  boiling-point  will 
destroy  all  except  the  bacterial  spores.  These  can  be  de- 
stroyed with  eertainty  only  by  prolonging  the  period  of 
exposure  to  212°  F.  for  a  number  of  hours.  This  is  not 
practical,  and  therefore  other  methods  must  be  used. 

The  culture  medium  in  appropriate  containers  is  placed 
in  a  steamer,  so  that  the  containers  will  be  surrounded  by 
streaming  steam.  An  exposure  for  fifteen  minutes  after  the 
temperature  of  the  medium  has  reached  that  of  the  steam 
will  suffice  to  kill  everything  except  the  bacterial  spores. 
If  the  medium  is  now  placed  at  ordinary  room  temperature, 
the  resistant  spores  will  germinate  within  a  few  hours,  and 
the  resulting  vegetative  cells  may  then  be  readily  destroyed 
by  a  second  heating.  In  practice,  three  exposures  are  made 
on  successive  days.  The  process  is  called  intermittent 
sterilization. 

If  the  temperature  of  the  steam  can  be  raised,  it  will,  of 
course,  have  a  more  destructive  effect  on  the  spores.  This 
is  done  by  placing  the  media  in  their  containers  in  a  steam- 


CULTIVATION  OF  MICROORGANISMS        37 

tight  apparatus.  Steam  is  generated  therein,  and  the  air 
is  allowed  to  escape  so  that  the  entire  space  will  be  filled 
with  steam.  The  chamber  is  then  closed.  The  tempera- 
ture obtained  will  depend  on  the  steam-pressure.  A 
steam-pressure  of  15  pounds  to  a  square  inch  yields  a  tem- 
perature of  120°  C.  (248°  F.).  Exposure  for  fifteen  min- 
utes to  this  temperature  is  usually  sufficient  to  sterilize  the 
media.  Where  any  amount  of  organic  matter  is  to  be  steril- 
ized, the  latter  method  is  used,  as  in  bacteriological  labora- 
tories and  in  canning  factories.  The  apparatus  employed 
is  ordinarily  termed  an  autoclave. 

The  same  method  can  be  used  for  the  sterilization  of  glass 
and  metal  objects,  and  of  clothing. 

The  culture  media  rendered  sterile  can  be  kept  for  an  in- 
definite time  if  protected  from  contamination  by  micro- 
organisms and  from  desiccation. 

Sterilization  by  dry  heat. — It  is  sometimes  more  con- 
venient to  use  dry  lieat,  such  as  that  of  an  oven,  for  the 
sterilization  of  objects  that  will  not  be  injured  thereby,  as 
glass  and  metals.  Dry  heat  is  far  less  destructive  to  life 
than  is  moist  heat.  It  is  thus  necessary  to  prolong  the  pe- 
riod of  exposure  and  to  increase  the  temperature  over  that 
used  in  the  autoclave  in  order  to  insure  sterilization.  A 
temperature  of  150°  to  170°  C.  (302-338°  F.)  must  be 
maintained  for  an  hour.  All  organic  matter  will  be  in- 
jured by  such  treatment. 

Small  objects  that  will  not  be  injured  by  heat  may  be 
sterilized  in  the  direct  flame  of  a  gas-burner.  The  needles 
used  for  transferring  bacteria  from  one  culture-tube  to 
another  in  the  laboratory  are  thus  rendered  germ-free. 

Sterilization  by  filtration. — It  is  essential  that  sterilized 
culture  media  and  other  organic  materials  be  protected 
from  contamination  after  treatment.  In  the  canning  in- 
dustry this  is  accomplished  b^  hermetically  sealing  the  con- 


38  AGRICULTURAL  BACTERIOLOGY 

tainer.  Such  a  method  is  impossible  in  the  laboratory, 
where  glass  containers  must  be  used  which  must  be  easily 
opened  and  closed,  and  yet  be  protected  from  contamina- 
tion. This  is  accomplished  by  plugging  the  tubes  and 
flasks  with  cotton  wool.  The  air  will  pass  freely  into  the 
container,  but  all  definite  bodies  such  as  microorganisms 
will  be  removed.  The  air  is  thus  effectively  sterilized.  If 
the  cotton  becomes  damp,  molds  may  grow  on  it  and  will 
soon  penetrate  it,  thus  contaminating  the  contents  of  the 
vessel. 

AVater  and  many  other  liquids  can  be  sterilized  by  passage 
through  filters  of  unglazed  porcelain.  Such  a  process  is 
sometimes  used  for  the  sterilization  of  culture  media  that 
would  be  so  altered  by  heating  as  to  be  rendered  worthless. 

Sterilization  by  chemicals  is  possible,  but  can  not  be  used 
in  the  laboratory ;  for  if  chemicals  are  added  to  the  culture 
media,  they  can  not  be  removed  or  rendered  non-effective 
so  as  to  permit  the  growth  of  bacteria  in  the  media. 

Isolation  of  pure  cultures  of  bacteria. — As  previously 
stated,  little  can  be  learned  concerning  the  relation  of  spe- 
cific kinds  of  organisms  to  a  particular  type  of  decompo- 
sition or  to  disease  production  until  the  organism  in  ques- 
tion has  been  separated  from  all  other  kinds,  and  thus  a 
pure  culture  obtained. 

The  most  common  way  of  securing  such  pure  cultures 
is  by  the  use  of  gelatin  or  agar.  The  medium  is  melted  and 
cooled  to  45°  C.  (113°  F.),  at  which  temperature  agar 
remains  liquid,  and  which  is  not  injurious  to  any  of  the 
bacteria.  A  small  amount  of  the  material  from  which  one 
desires  to  isolate  the  pure  culture  is  intimately  mixed  with 
the  liquid  medium.  This  is  then  poured  into  a  shallow  flat 
glass  dish,  which  is  allowed  to  cool.  The  agar  quickly  solid- 
ifies, holding  the  contained  organisms  in  .place.  In  the 
favorable  nutrient  medium,  growth  occurs  with  the  forma- 


CULTIVATION  OF  MICROORGANISMS 


39 


tion  of  a  mass  of  cells  sufificiently  large  to  be  visible  to  the 
unaided  eye.     Such  masses  are  termed  colonies. 

Each  colony  represents  the  progeny  of  a  single  cell  or  a 
group  of  cells.     The  colonies  of  many  kinds  of  bacteria  ex- 


Fig.  IG.     A  Plate  Culture 
Each  of  the  spots  or  colonies  on  the  plate  has  resulted  from  the  growth  of  a 
single  cell  or  group  of  cells  of  the  same  kind  in  the  substance  with  which  the 
plate    was    seeded.      Plate    cultures    are    used    for    determining    the    number    of 
bacteria  in  various  substances  and  for  the  isolation  of  pure  cultures  of  bacteria 

hibit  more  or  less  characteristic  appearances,  with  reference 
to  the  size  of  the  colony,  its  shape,  the  nature  of  its  edge, 
and  its  interior  structure.  These  are  termed  cultural  char- 
acteristics. The  colonies  resulting  from  cells  that  were  on 
the  immediate  surface  of  the  medium  or  very  close  to  it 
give  rise  to  surface  colonies.  These  exhibit  the  more  char- 
£icteristic  appearances,  since  the  growth  can  develop  freely. 


40  AGRICULTUEAL  BACTERIOLOGY 

The  deep  colonies  that  result  from  the  growth  of  cells  em- 
bedded in  the  agar  must  push  the  culture  medium  aside  in 
order  to  make  room  for  the  mass  of  cells.  Since  the  colony 
is  under  considerable  pressure,  it  can  not  develop  freely. 
The  form  of  such  colonies  is  most  commonly  lenticular,  or 
spherical. 

It  is,  of  course,  essential  that  all  materials  and  objects 
used  in  making  the  plate  culture,  as  it  is  commonly  called, 
be  sterile,  with  the  exception  of  the  material  to  be  exam- 
ined, otherwise  one  could  not  be  assured  of  the  exact  source 
of  the  resulting  growth.  It  is  also  essential  that  the  colo- 
nies be  not  too  numerous,  otherwise  their  size  will  be  limited 
by  the  competition  for  food.  It  is  usual  to  prepare,  not  a 
single  plate  culture,  but  several  plates  containing  varying 
amounts  of  the  material,  so  that  on  some  one  of  the  plates 
the  resulting  colonies  will  not  be  too  numerous  for  success- 
ful isolation  of  the  pure  cultures. 

A  minute  portion  of  a  colony  may  be  transferred  to  a 
tube  of  sterile  agar  or  other  appropriate  media,  producing 
what  is  called  a  tuhe  culture.  The  exact  form  of  the  organ- 
ism under  observation  can  now  be  observed  under  the 
microscope,  and  its  physiological  properties  determined  by 
seeding  it  on  various  kinds  of  culture  media  and  noting  the 
resultant  growth.  The  growth  of  the  organism  in  the  tube 
culture  soon  ceases,  owing  to  the  accumulation  of  its  waste 
products  or  to  the  exhaustion  of  food.  The  cells  will  re- 
main alive  for  varying  periods  of  time,  depending  on  the 
organism.  The  culture  can  be  kept  alive  by  furnishing  it 
with  fresh  food  through  the  transfer  of  a  few  of  the  cells  to 
a  new  tube  of  nutrient  medium.  Such  cultures  form  the 
so-called  stock  cultures^  and  are  the  pure  seed  supply  of  the 
bacteriologist. 

In  many  instances  it  is  impossible  to  isolate  an  organism 
from  its  native  habitat  by  the  plate-culture  method.     This 


CULTIVATION  OF  MICROORGANISMS         41 

method  will  be  successful  only  when  the  desired  organism 
is  present  in  approximately  as  great  numbers  as  the  other 
bacterial  forms  that  can  develop  on  the  plate  culture.  If 
only  a  few  of  the  organisms  are  present,  it  will  usually  be 
necessary  to  seed  some  special  selective  medium  that  is  more 
favorable  for  the  desired  organism  than  for  the  other  types 
with  which  it  may  be  associated.  This  will  enable  the  or- 
ganism in  question  to  gain  the  ascendancy  in  the  culture, 
which  can  then  be  plated  with  assured  success. 

An  animal  that  is  susceptible  to  a  disease  may  be  inocu- 
lated with  a  mixture  of  kinds  of  bacteria  among  which  the 
producer  of  the  disease  is  present.  The  body  of  the  animal 
will  act  as  a  selective  medium,  and  from  its  tissues  a  pure 
culture  can  often  be  obtained.  Many  modifications  are  em- 
ployed to  obtain  pure  cultures  of  some  of  the  bacteria. 
More  extended  texts  on  laboratory  methods  must  be  con- 
sulted for  the  methods  employed. 

Quantitative  methods. — The  plate  culture  is  also  used  for 
the  determination  of  the  number  of  microorganisms  in  any 
material.  If  a  known  amount  of  the  material  is  added  to 
the  melted  nutrient  agar  or  gelatin,  the  number  of  colonies 
developing  in  the  plate  culture  can  be  counted,  and  from 
these  results  the  bacterial  content  of  the  original  material 
may  be  determined.  Each  colony  must  have  developed 
from  at  least  one  cell.  It  is  thus  possible  to  obtain  a  num- 
ber that  will,  as  a  rule,  approximate  the  number  of  cells 
actually  present  in  the  material  used.  The  method  is  used 
constantly  in  the  control  of  water  and  milk  supplies. 

It  is,  of  course,  impossible  to  obtain  a  medium  that  will 
enable  all  kinds  of  bacteria  that  may  be  present  in  such 
materials  as  milk  or  water  to  develop.  The  results  thus 
obtained  represent  only  the  number  of  organisms  that  are 
able  to  grow  under  the  conditions  present  in  the  culture 
plate.     It  is  usually  possible  to  adjust  the  conditions  so 


42  AGRICULTURAL  BACTERIOLOGY 

that  the  organisms  that  one  desires  to  study  will  develop, 
and  thus  the  plate-culture  method  of  determining  bacteria 
is  of  great  value  in  spite  of  its  limitations. 

Microscopic  examination. — An  object  having  dimensions 
less  than  0.2  micron  can  not  be  demonstrated  even  under  a 
high-powered  microscope.  Some  of  the  bacteria  approach 
this  limit.  Indeed,  the  great  majority  of  the  spheres  are 
less  than  one  micron  in  diameter.  It  is  therefore  essential 
to  employ  instruments  that  will  give  the  maximum  degree 
of  magnification;  but,  since  magnification  is  secured  only 
with  a  reduction  in  illumination,  a  practical  limitation  is 
placed  on  the  possible  increase  in  the  magnifying  power  of 
the  microscope. 

The  two  developments  of  the  microscope  that  greatly  ac- 
celerated the  development  of  bacteriology  were  concerned 
with  an  increased  illumination  of  the  object.  The  first  was 
the  immersion  objective,  which  prevents  the  refraction  or 
bending  of  the  rays  of  light  as  they  pass  from  the  glass  on 
which  the  object  to  be  examined  is  placed,  into  the  air. 
This  is  accomplished  by  placing  a  drop  of  liquid  having  the 
same  index  of  refraction  as  glass  between  the  lens  and  the 
glass  slide.  Cedar  oil  dissolved  in  xylol  is  used  for  this 
purpose. 

The  light  rays  are  reflected  from  the  mirror  through  the 
object  into  the  lens  of  the  microscope.  The  Abbe  con- 
denser is  a  series  of  lenses  placed  beneath  the  stage  of  the 
microscope  which  concentrates  the  light  rays  coming  from 
a  certain  area  of  the  mirror  and  focuses  them  on  a  much 
smaller  area  of  the  object,  thus  illuminating  it  brightly. 

Examination  of  unstained  bacteria. — The  motility  of 
bacteria  can  be  determined  only  by  examining  a  liquid  that 
contains  the  living  cells.  For  this  purpose,  a  drop  of  the 
liquid  containing  the  bacteria  is  placed  on  a  very  thin  piece 
of  glass,  l^nown  as  a  cover-glass,  which  is  inverted  over  a 


STUDY  OF  MICROORGANISMS  43 

cavity  ground  in  a  thicker  piece  of  glass,  the  slide.  The 
evaporation  of  the  drop  in  the  unsealed  space  causes  cur- 
rents, the  effect  of  which  makes  it  difficult  to  determine 
whether  the  movement  of  the  contained  bacteria  is  a  really 
independent  one,  or  is  due  to  the  currents.  By  sealing  the 
edges  of  the  cover-glass  to  the  slide  with  vaseline,  evapora- 
tion is  prevented. 

All  finely  divided  matter  suspended  in  a  liquid  shows  a 
purely  physical  movement  known  as  the  Brownian  move- 
ment. Each  particle  has  a  trembling  or  vibratory  motion, 
but  no  progressive  movement  of  the  particles  from  place  to 
place  is  noted.  The  bacteria  are  sufficiently  small  to  show 
this  molecular  motion.  Those  forms  of  bacteria  that  are 
provided  with  flagella  have  the  power  of  independent  pro- 
gressive motion,  which  can  be  readily  demonstrated  under 
the  microscope. 

Staining. — The  live  bacteria  are  difficult  to  demonstrate 
in  any  material,  except  in  a  liquid  in  which  they  are  the 
only  bodies  in  suspension.  In  such  materials  as  milk,  blood, 
and  other  body  fluids,  the  recognition  of  bacteria  by  the 
microscope  is  impossible,  unless  the  material  can  be  so 
treated  as  to  differentiate  the  organisms  from  the  other 
materials  present.  This  is  done  by  staining  the  organisms 
with  solutions  of  certain  dyes.  The  material  to  be  exam- 
ined is  spread  in  a  thin  film  on  a  slide  or  cover-glass,  and 
allowed  to  dry.  The  film  is  then  treated  in  a  way  that  will 
cause  it  to  adhere  firmly  to  the  glass  when  it  is  subsequently 
moistened.  This  process  is  termed  ''fixing"  the  prepara- 
tion, and  is  accomplished  by  gently  heating  the  dried  film 
in  a  gas  flame  to  such  a  temperature  as  to  cause  the  protein 
to  coagulate,  or  by  treatment  with  some  chemical  that  will 
produce  the  same  eft'ect.  The  film  can  now  be  flooded  with 
a  dye  and  the  material  will  not  be  washed  from  the  slide. 

The  stains  most  commonly  used  are  the  aniline  dyes, 


44  AGRICULTURAL  BACTERIOLOGY 

which  were  first  discovered  accidentally  by  Perkin  in  Eng- 
land in  1856.  They  were,  however,  not  used  in  the  study 
of  the  bacteria  until  1876,  when  they  were  employed  by 
Weigert.  They  have  been  of  the  greatest  service  in  the  de- 
velopment of  bacteriology. 

The  bacteria  can  be  differentiated  from  the  other  mate- 
rials in  which  they  occur,  either  by  a  contrast  in  depth  of 
color,  or  by  staining  all  or  a  portion  of  the  bacteria  one 
color  and  the  other  materials  another  color.  The  first 
method  can  be  used  in  demonstrating  the  bacteria  in  milk ; 
a  film  of  milk  stained  with  methylene  blue  will  reveal  the 
bacteria  as  dark  blue  objects  in  a  light  blue  field.  The 
casein  and  albumen  form  the  background  of  the  prepara- 
tion. The  organisms  that  cause  tuberculosis  may  be  de- 
tected in  sputum,  milk,  and  in  other  materials  by  staining 
them  a  bright  red,  while  the  other  bacteria  and  the  mate- 
rial in  which  they  are  embedded  are  stained  blue.  The 
tubercle  bacilli  are  thus  differentiated  from  the  other  bac- 
teria and  the  background  of  the  preparation  in  a  striking 
way.  This  is  made  possible  by  a  property  of  the  tubercle 
bacillus  which  will  be  discussed  later. 

Stained  preparations  are  usually  employed  for  the  study 
of  the  morphology  of  bacteria,  for  the  demonstration  of 
spores  and  flagella.  The  spores  do  not  stain  as  easily  as  do 
the  vegetative  cells.  It  is  thus  possible  to  have  the  spores 
appear  as  a  bright  unstained  area  in  a  stained  cell.  If 
the  spores  have  been  set  free  by  the  dissolution  of  the  cell, 
they  will  appear  as  bright  oval  bodies  in  the  microscopic 
field. 

The  flagella  are  so  minute  that,  unless  their  apparent  di- 
ameter is  increased,  they  can  not  be  seen  with  the  micro- 
scope. They  can  be  made  visible  by  precipitating  some  dye 
on  them  and  thus  increasing  their  apparent  diameter. 

The  staining  properties  of  bacteria  aid  in  their  classifica- 


STUDY  OF  MICROORGANISMS  45 

tion.  The  most  valuable  of  the  methods  used  for  this  pur- 
pose is  that  devised  by  Gram.  If  bacterial  preparations  are 
stained  with  gentian  violet  dissolved  in  a  saturated  solution 
of  aniline  oil  in  water,  and  then  treated  with  iodine  dis- 
solved in  a  solution  of  potassium  iodide,  the  combination 
of  the  protoplasm  of  the  cell  and  the  dye  is,  in  the  ease  of 
certain  orjranisms,  of  such  a  nature  as  to  be  soluble  in  alco- 
hol; in  the  case  of  other  bacteria  it  is  insoluble.  The  latter 
retain  in  the  presence  of  alcohol  the  color  imparted  to  them 
by  the  d.ye,  and  are  termed  Gram-positive  organisms.  The 
others  are  called  Gram-negative^  since  the  color  is  removed 
by  washing  the  preparation  in  alcohol.  This  method  is  of 
value  in  demonstrating  Gram-positive  bacteria  in  tissues 
that  are  themselves  Gram-negative. 

Systematic  study  of  bacteria. — The  classification  of 
higher  plants  and  animals  and  their  identification  is  based 
wholly  upon  their  morphology,  their  form,  and  their  struc- 
ture. In  the  case  of  such  simple  organisms  as  the  bacteria, 
the  variation  in  form  is  so  slight  as  to  make  this  character 
of  limited  value  in  the  study  and  identification  of  a  par- 
ticular pure  culture.  Many  different  kinds  of  bacteria  are 
so  alike  in  the  form  of  the  cell  itself  that  it  becomes  neces- 
sary to  include  other  characteristics  in  differentiating  one 
type  from  another. 

Cultural  characteristics. — The  appearance  of  a  mass  of 
cells  that  has  developed  in  or  on  a  culture  medium  is  often 
so  characteristic  that  it  can  be  used  in  separating  one  spe- 
cies from  another.  For  example,  if  a  pure  culture  pro- 
duces a  uniform  turbidity  in  a  liquid,  it  is  evident  that  the 
cells  will  be  found  as  single  cells,  or  in  very  small  aggre- 
gates. If  the  growth  is  massed  at  the  top  or  the  bottom  of 
the  culture  medium,  it  implies  that  the  cell-aggregates  will 
be  large,  and  that  the  cells  may  be  found  in  long  chains, 
or  in  zoogloea-like  masses.     The  medium  may  remain  per- 


46  AGRICULTURAL  BACTERIOLOGY 

fectly  clear  except  for  the  growth  at  the  surface  or  bottom. 
The  culture  growth  may  vary  widely  in  its  profuseness, 
from  that  which  is  invisible  to  the  eye  to  one  that  may 
occupy  a  considerable  part  of  the  volume  of  the  medium. 
The  profuseness  of  growth  is  a  reflection  of  the  morphology 
and  physiology  of  the  organism  concerned.     If  pronounced 
capsules   are  formed,   the  mass   of   growth   will   be   large. 
Again,  if  the  by-products  are  extremely  toxic  to  the  organ- 
ism, growth  can  continue  but  a  short  time ;  while,  if  they  are 
not  toxic,  the  growth  may  be  limited  only  by  lack  of  food. 
The  consistency  of  the  growth,  whether  moist  or  dry, 
friable  or  slimy,  is  also  noted,  as  is  the  color.     The  great 
majority  of  the  bacteria  produce  a  grayish  white  growth, 
which  is  more  or  less  opaque.     Some  produce  pigments,  and 
are  called  chromogenic  organisms.     The  most  common  col- 
ors noted  are  yellows,  varying  from  a  pale  lemon  to  a  deep 
orange.     Blue,  violet,  green,  red,  brown,  and  black  are  less 
common.     In  some  instances  the  pigment  is  a  by-product, 
produced  under  certain  conditions  of  growth  and  not  under 
others.     Its  production  is  thus  not  an  essential  part  of  the 
physiology  of  the  cell.     In  other  cases  it  is  a  constant  prop- 
erty, and  undoubtedly  is  a  part  of  the  vital  processes  of  the 
cell.     If  the  pigment  is  soluble  in  water,  the  medium  in 
which  the  organism  is  growing  will  be  colored.     If  it  is  in- 
soluble, the  growth  alone  is  colored.     Among  the  manifes- 
tations of  the   chromogenic  bacteria  that  have   attracted 
especial  attention  are  green  pus,  blue  milk,  and  bright  red 
spots  on  bread,  the  latter  due  to  B.  prodigiosus. 

The  relation  of  the  organism  to  air  will  determine  the 
location  of  its  growth  in  culture  media,  and  thus  affect  the 
appearance  of  the  culture.  The  by-products  of  the  organ- 
ism will  also  aid  in  determining  the  cultural  characteristics. 
The  formation  of  gas  is  an  example. 
Physiological  characteristics. — In  the  detailed  study  of 


STUDY  OF  MICROORGANISMS  47 

an  organism,  attention  is  directed  chiefly  to  the  chemical 
changes  that  it  produces  in  the  substances  in  which  it  is 
growing,  i.  e.,  to  the  biochemical  properties  of  the  organism. 
Culture  media  are  prepared  containing  definite  chemical 
substances,  and  the  products  formed  therefrom  are  deter- 
mined. The  points  to  which  attention  is  chiefly  directed 
are  the  fermentation  of  various  carbohydrates  with  the  for- 
mation of  acids,  alcohols,  and  gases;  as  well  as  the  action 
of  the  organism  on  different  proteins,  e.  g.y  casein  and  gela- 
tin. The  ability  of  the  organism  to  produce  disease  in 
plants  and  animals  may  also  be  studied. 

The  final  criterion  in  the  identification  of  any  organism 
is  the  determination  of  its  ability  to  cause  a  specific  effect. 
Thus  the  identification  of  the  anthrax  bacillus  rests  on  the 
production,  in  animals  known  to  be  susceptible  to  anthrax, 
of  a  disease  that  has  the  characteristics  of  anthrax.  An 
organism  may  have  the  same  morphology,  the  same  cul- 
tural characteristics,  and  the  same  physiological  character- 
istics, as  determined  by  the  usual  laboratory  tests,  as  the 
true  anthrax  bacillus;  but,  unless  it  produces  death  in 
guinea-pigs,  with  certain  definite  changes  in  the  tissues,  it 
can  not  be  identified  as  the  anthrax  organism.  The  identi- 
fication of  a  pure  culture  of  bacteria  is  a  difficult  task*,  in 
the  solution  of  which  all  the  tests  that  science  has  devised 
may  be  used. 


CHAPTER  V 

PHYSIOLOGY  OF  MICROORGANISMS 

In  a  general  way,  the  simple  presence  of  microorganisms 
has  no  significance,  as  far  as  the  decomposition  of  organic 
matter  is  concerned.  Decomposition  always  implies  the 
growth,  the  proliferation,  of  the  organism.  Two  problems 
present  themselves  daily  to  almost  every  individual.  One 
is  connected  with  the  prevention  of  the  growth  of  organ- 
isms in  order  that  organic  materials  may  be  preserved ;  the 
other  is  the  facilitation  of  the  growth  of  organisms  in  order 
that  the  chemical  change  that  they  cause  may  be  hastened. 
The  conditions  favoring  or  retarding  the  growth  of  micro- 
organisms thus  become  of  great  practical  importance. 

Moisture. — Water  is  an  essential  condition  for  the  de- 
velopment of  all  life.  It  makes  up  a  large  part  of  the 
weight  of  every  organism;  it  is  needed  for  the  transporta- 
tion of  the  food  and  waste  products.  It  is  impossible  to 
make  any  general  statement  in  regard  to  the  amount  of 
water  that  must  be  present  before  growth  can  take  place. 
Some  types  of  materials  hold  water  in  such  a  way  that  the 
organisms  can  not  make  use  of  it.  The  material  is  then 
said  to  be  physiologically  dry.  Bacteria  can  grow  in  butter 
containing  15  per  cent,  of  water,  while  they  can  not  grow 
in  most  types  of  organic  matter  unless  a  much  greater  per- 
centage of  water  is  present.  The  reduction  of  the  water 
content  of  organic  matter  is  the  most  common  way  of  pre- 
serving it  from  the, attacks  of  microorganisms. 

The  growth  of  microorganisms  may  be  prevented  in  the 
presence  of  large  amounts  of  water  by  its  content  of  raate- 

48 


PHYSIOLOGY  OF  MICROORGANISMS  49 

rials  in  solution.  The  cell  must  have  an  internal  pressure — 
i.  e.y  it  must  be  turgid — before  growth  can  take  place.  This 
pressure  is  known  as  o.wiotic  pressure,  and  is  due  to  the 
fact  that  the  concentration  of  the  liquid  in  the  cell  is 
greater  than  that  of  the  liquid  in  which  the  cell  is  found. 
The  protoplasmic  layer  that  is  in  direct  contact  with  the 
cell  wall  functions  as  a  semi-permeable  membrane,  which 
will  allow  the  passage  of  certain  substances  in  and  out  of  the 
cell  freely,  and  will  not  permit  others  to  pass.  Certain  of 
the  cell  constituents  are  thus  prevented  from  leaving  the 
cell.  In  an  effort  to  maintain  an  equilibrium  of  concen- 
tration inside  and  outside  of  the  cell  with  reference  to  these 
compounds,  water  is  drawn  into  the  cell.  The  passage  of 
water  into  the  cell  creates  the  internal  pressure.  If  a  cell 
is  placed  in  a  solution  of  some  material  that  can  not  pass 
into  the  cell  on  account  of  this  semi-permeable  membrane, 
water  will  be  withdrawn  from  the  cell  to  assist  in  establish- 
ing an  equilibrium  of  concentration.  The  internal  pres- 
sure of  the  cell  will  be  destroyed  by  this  process.  The  cell 
is  then  said  to  be  flaccid  or  plasmolyzed.  In  this  condition 
no  growth  can  take  place.  The  plasmolyzed  condition  may 
be  a  permanent  one,  or  it  may  be  overcome  by  the  slow 
passage  of  the  substance  into  the  cell  and  the  reestablish- 
ment  of  a  turgid  condition. 

The  yeasts  are  more  resistant  to  the  effect  of  materials  in 
solution  than  are  the  bacteria.  Many  of  them  can  grow  in 
an  almost  saturated  solution  of  cane  sugar,  while  a  15  per 
cent,  solution  will  inhibit  the  growth  of  most  bacteria.  The 
molds  are  still  more  resistant  to  the  action  of  concentrated 
solutions.  In  fact,  the  inhibition  of  mold  growth  by  in- 
creasing the  concentration  of  the  liquid  by  the  addition  of 
sugar  or  salt  is  so  slight  as  to  be  of  little  importance.  The 
molds  are  likewise  able  to  grow  on  materials  from  which 
bacteria  and  yeasts  can  obtain  no  water.     In  other  words,  a 


50  AGRICULTURAL  BACTERIOLOGY 

material  may  be  physiologically  dry  for  one  form  of  life  and 
not  for  another.  The  growth  of  molds  on  bread,  cheese, 
dried  meats,  paper,  and  clothing  is  evidence  of  their  ability 
to  grow  in  the  presence  of  a  small  percentage  of  water. 

If  a  cell  is  transferred  from  a  concentrated  solution  to 
one  that  is  less  concentrated,  the  water  will  be  drawn  into 
the  cell  and  may  cause  the  rupture  of  the  cell  wall.  The 
term  plasmotypsis  is  applied  to  this  process. 

Many  of  the  bacteria  can  not  withstand  desiccation,  the 
cells  being  almost  immediately  destroyed.  Still  others  can 
remain  alive  in  a  dried  condition  for  long  periods  of  time. 
Their  resistance  to  desiccation  becomes  of  importance  in 
disease  transmission.  The  bacterial  spores  are  extremely 
resistant  to  drying.  Yeasts  are,  in  general,  less  easily  in- 
jured by  desiccation  than  are  the  bacteria.  The  mold 
spores  are  very  resistant  to  drying. 

Temperature. — As  is  well  known,  decomposition  goes  on 
more  rapidly  as  the  temperature  is  increased,  up  to  a  cer- 
tain limit.  This,  of  course,  implies  that  the  growth  of  the 
microorganisms  is  accelerated  as  the  temperature  rises. 
The  temperature  at  which  any  organism  thrives  most  rap- 
idly is  known  as  the  optimum  temperature  for  that  organ- 
ism. As  the  temperature  changes  from  the  optimum,  the 
rate  of  growth  decreases.  As  a  rule,  a  few  degrees  above 
the  optimum  temperature,  growth  is  no  longer  possible. 
The  maximum  temperature  has  been  reached.  As  the  tem- 
perature falls  below  the  optimum,  the  rate  o.f  growth  is 
reduced  until  a  point  is  reached  at  which  it  ceases.  This 
is  known  as  the  minimum  temperature,  and  is,  as  a  rule, 
far  below  the  optimum  temperature. 

The  temperature  zone  in  which  growth  of  bacteria  is  pos- 
sible varies  widely  with  different  organisms.  In  the  case 
of  some,  it  is  but  a  few  degrees  in  extent;  with  others^  it 
may  be  very  wide,  ranging  from  the  freezing-point  to  that 


PHYSIOLOGY  OF  MICROORGANISMS  51 

of  the  animal  body.  The  great  majority  of  microorganisms 
have  their  optimum-growth  temperature  between  20°  and 
40°  C.  (68°-] 04°  F.).  The  term  mesophilic  is  applied  to 
these.  For  others  the  optimum  is  lower;  these  are  called 
psychrophilic,  while  those  that  grow  at  high  temperatures 
are  called  thernwphilic.  The  minimum  temperature  for  the 
psychrophilic  organisms  is  usually  below  0°  C.  (32°  F.). 
The  maximum  temperature  for  the  thermophilic  may  reach 
70°  C.  (158°  F.),  a  temperature  at  which  most  vegetative 
bacteria  are  quickly  destroyed.  It  is  thus  seen  that  the 
temperature  zone  in  which  the  growth  of  bacteria  is  pos- 
sible is  an  extremely  wide  one,  extending  from  below  the 
freezing-point  of  water  to  what  are  ordinarily  termed  scald- 
ing temperatures.  No  one  organism  is  able  to  grow  through 
this  entire  range.  Organisms  that  are  able  to  grow  at  high 
and  others  that  are  able  to  grow  at  low  temperatures  are 
common  in  soil  and  in  the  feces  of  animals. 

Organisms  can  grow  below  the  freezing-point  of  water 
only  when  the  freezing-point  is  depressed  by  the  presence 
of  soluble  material  in  the  water  of  the  food. 

The  temperature  zone  of  existence  is  far  wider  than  that 
of  growth.  Freezing  does  not  normally  destroy  either  vege- 
tative bacteria  or  the  spores.  If  the  organisms  are  kept  in 
a  frozen  condition  for  long  periods,  they  gradually  die. 
The  death  rate  is  so  slow  that  food  removed  from  cold  stor- 
age may  spoil  as  quickly  as  it  would  have  done  at  the  same 
temperature  before  being  frozen.  Indeed,  the  spoiling  is 
often  more  rapid  in  certain  foods  that  are  so  changed  by 
freezing  as  to  adapt  them  better  for  the  invasion  and  growth 
of  bacteria  therein.  Repeated  freezing  and  thawing  is 
more  harmful  than  being  kept  continuously  in  a  frozen  con- 
dition. Still  lower  temperatures  do  not  seem  to  have  much 
additional  effect. 

As  the  temperature  is  increased  above  the  maximum  for 


52  AGRICULTURAL  BACTERIOLOGY 

growth,  a  point  is  soon  reached  at  which  injury  to  the  cells 
takes  place.  The  weaker  cells  are  first  destroyed ;  the  more 
resistant  only  as  the  heat  is  applied  for  a  longer  period 
or  a  higher  temperature  is  used.  The  point  at  which  all 
of  the  cells  of  a  given  culture  are  destroyed  is  known  as  the 
thermal  death  point.  This  temperature  will  depend  on  the 
length  of  exposure  to  heat,  and  on  the  amount  of  moisture 
present.  The  smaller  the  percentage  of  water,  the  less  in- 
jurious will  be  the  effect  of  the  heat.  Heat  injures  the 
cell  through  coagulation  of  the  protoplasm.  The  tempera- 
ture required  to  cause  coagulation  rises  rapidly  as  the  water 
content  of  the  cells  decreases.  This  fact  is  the  reason  for 
the  greater  effectiveness  of  moist  heat  as  compared  -with  dry 
heat  in  sterilizing  processes. 

The  chemical  reaction  of  the  liquid  is  also  a  factor  in  de- 
termining the  destructive  action  of  heat  on  microorganisms. 
In  an  acid-reacting  liquid  they  are  .more  easily  destroyed 
than  in  a  neutral  solution.  Bacterial  spores,  as  has  been 
stated,  are  extremely  resistant  to  heat. 

Relation  to  oxygen. — Oxygen  is  an  essential  element  for 
the  growth  of  all  life.  The  higher  forms  of  life,  both  plant 
and  animal,  are  adjusted  to  rather  definite  percentages  of 
oxygen  in  the  air.  This  is  not  true  of  the  microorganisms 
as  a  class.  Some  can  grow  in  the  total  absence  of  free  oxy- 
gen; still  others  can  grow  in  percentages  far  above  that  of 
the  atmospheric  air. 

The  term  anaerobic  is  applied  to  those  that  can  grow  in 
the  absence  of  free  oxygen.  They  can  also  grow  in  the  pres- 
ence of  reduced  amounts  of  free  oxygen.  When  they  grow 
in  the  absence  of  free  oxygen,  they  must  draw  their  oxygen 
supply  from  combined  sources,  as  from  the  sugars,  nitrates, 
or  sulphates.  In  this  mode  of  securing  oxygen,  they  are 
liot  unlike  the  unit  cells  of  the  animal  body  that  derive  their 


PHYSIOLOGY  OF  MICROORGANISMS         53 

oxygen  from  a  combined  source,  the  oxyhemaglobin  of  the 
blood. 

The  bacteria  that  can  grow  only  in  the  presence  of  rela- 
tively large  amounts  of  oxygen  are  termed  aerobic.  In 
liquids  the  growth  of  such  organisms  will  be  confined  to  the 
surface.  The  organisms  tliat  can  grow  through  a  wide 
range  with  respect  to  the  amount  of  oxygen,  from  a  total 
absence  to  that  of  atmospheric  air,  are  called  facultdtive. 
If  the  organism  grows  better  in  the  absence  of  free  oxygen 
than  in  its  presence,  it  is  termed  a  facultative  aerobe.  If 
the  reverse  is  true,  the  term  facultative  anaerobe  is  used. 
The  facultative  bacteria  make  up  the  greater  part  of  the 
known  species. 

The  cultivation  of  anaerobic  bacteria  is  accomplished  by 
replacing  the  air  of  the  culture  container  with  hydrogen, 
nitrogen,  or  carbon-dioxide,  by  absorbing  the  oxygen  of  the 
air  with  some  substance  such  as  an  alkaline  solution  of 
pyrogallic  acid.  ^lost  of  them  can  be  grown  in  appropriate 
culture  media  without  the  artificial  exclusion  of  air.  It 
seems  probable  that  in  the  soil,  and  in  other  places  in  na- 
ture, the}'  can  grow  in  the  presence  of  larger  amounts  of 
oxygen  than  will  permit  their  growth  in  the  laboratory. 

The  yeasts  are  facultative.  It  seems,  however,  that, 
while  growth  may  go  on  for  a  period  in.  the  absence  of  oxy- 
gen, it  can  not  continue  for  an  indefinite  time,  as  is  ap- 
parently true  with  the  anaerobic  bacteria. 

The  molds  are  all  aerobic,  a  fact  that  becomes  of  great 
importance  in  food  preservation. 

Reaction. — The  true  chemical  reaction,  the  relative  num- 
ber of  liydrogen  ions  as  compared  to  hydroxyl  ions,  is  a 
factor  of  great  importance  in  influencing  the  growth  of 
microorganisms.  The  bacteria,  as  a  rule,  grow  best  in  neu- 
tral materials.     The  yeasts  will  grow  in  neutral  substances. 


54  AGRICULTURAL  BACTERIOLOGY 


Fig.  17.     Effect  of  Acid  on  Bacteria  and  Yeasts 

The  lighter  portion  of  the  plate  contains   an   acid  agar,   the  darker  portion  a 

neutral    agar.     Threads   carrying   bacteria    and   yeast   respectively   were    placed 

on  the  plate.     The  bacteria  on  the  lower  thread  grew  only  on  the  neutral  agar 

while  the  yeast  grew  on  both  but  more  profusely  on  the  acid  medium 

and  also  in  those  that  are  quite  acid,  as  in  fruit  juices. 
The  molds  will  tolerate  a  still  greater  acidity. 

Light. — One  ordinarily  thinks  of  light  as  favorable  to 
the  development  of  animals.  It  is,  of  course,  essential  for 
the  growth  of  the  green  plants,  since  from  it  they  secure 
their  energy.  Any  portion  of  the  animal  body  not  pro- 
tected by  a  covering  or  by  a  pigment  in  the  cells  will  be 
quickly  injured  by  the  direct  rays  of  the  sun.  Sunburn  is 
evidence  of  this  action.  By  the  development  of  pigment 
or  the  darkening  of  the  skin,  the  injurious  action  of  light 
is  prevented.  The  cells  of  microorganisms  are  likewise 
easily  destroyed  by  the  direct  rays  of  the  sun.     Artificial 


PHYSIOLOGY  OF  MICROORGANISMS         55 

light  is  used  for  the  destruction  of  bacteria  in  water.  The 
source  of  light  is  the  mercury-vapor  lamp,  which  is  espe- 
cially high  in  violet  and  ultra-violet  rays,  which  are  most 
efficient  in  the  destruction  of  bacteria.     Glass  prevents  the 


Effect  of  Light 


Tlie  agar  plate  was  seeded  over  the  entire  surface  with  bacteria.  The  center 
of  the  plate  was  protected  and  tlie  plate  was  exposed  to  the  direct  rays  of  the 
sun    for  one   hour.      All   organisms    except  those   protected   from   the   sun    have 

been  killed. 

passage  of  these  rays  to  such  an  extent  as  to  make  a  lamp 
with  a  glass  tube  of  little  value,  while  one  with  a  quartz 
tube  will  be  very  effective. 

The  germicidal  action  of  sunlight  in  the  destruction  of 
disease-producing  organisms  in  houses  and  stables  has  been 
greatly  over-emphasized.  It  requires  but  a  thin  layer  of 
dust  to  destroy  the  effect  of  the  light.     Again,  but  a  small 


56  AGRICULTURAL  BACTERIOLOGY 

portion  of  the  walls  inclosing  any  space  is  exposed  to  the 
sun. 

Chemicals. — Many  chemicals,  both  inorganic  and  organic, 
are  toxic  to  animals.  The  same  is  true  of  microorganisms, 
and  in  a  general  way  the  same  chemicals  are  injurious  to 
both  forms  of  life.  The  term  'disinfectant  is  applied  to 
those  substances  that  have  a  marked  action  on  microorgan- 
isms; to  those  that  have  a  less  pronounced  effect  the  term 
antiseptic  is  applied.  The  action  of  the  latter  may  be 
limited  to  the  prevention  of  growth.  When  such  substances 
are  used  in  foods,  they  are  called  preservatives.  A  discus- 
sion of  the  various  chemicals  used,  in  one  connection  or 
another,  will  be  included  later. 

Food. — The  food  of  bacteria,  yeasts,  and  molds  must  be 
soluble  in  water,  otherwise  it  can  not  pass  into  the  cell.  All 
naturally  occurring  organic  matter  serves  as  food  for  some 
kind  of  an  organism;  and  yet,  much  of  it  is  insoluble  in 
water.  The  question  then  arises  as  to  how  the  insoluble 
material  can  be  used. 

The  animal  ingests  insoluble  food  and  prepares  it  for 
passage  through  the  intestinal  wall  by  pouring  into  the 
alimentary  tract  at  various  levels  agents  that  change  the 
insoluble  food  into  soluble  compounds.  These  digestive 
agents  are  known  as  enzymes.  One  acts  upon  starch,  an- 
other on  protein,  still  another  on  fats.  In  fact,  each  animal 
is  provided  with  such  an  array  of  enzymes  as  will  enable  it 
to  use  all  the  compounds  of  its  normal  food. 

The  cell  of  the  microorganism  may  be  compared  to  the 
animal  in  this  respect.  It  forms  enzymes  that  diffuse  into 
the  material  in  which  the  cell  finds  itself,  and  that  change 
the  insoluble  compounds  into  soluble  ones.  This  is  a  proc- 
ess of  decomposition.  It  is  a  form  of  decomposition,  how- 
ever, in  which  energy  is  not  dissipated.  If  it  were,  it 
would  be  a  most  wasteful  process  as  far  as  the  organism  is 


PHYSIOLOGY  OP  MICROORGANISMS         57 


FijT.  10.     Enzyme  Action 

The  light  portion  of  the  phite  is  due  to  the  presence  of  casein  in  the  agar.     The 

digesting  enzyme  has  acted  on  the  casein  not  only  in  contact  with  the  bacteria 

which  form  the   white  streak,   but  on  that  a  distance  away.     The  enzyme   has 

changed  the  casein  to  soluble  products  which  can  pass  into  the  cells 

concerned.  The  processes  that  go  on  inside  the  cell,  and 
that  are  connected  with  the  assimilation  of  the  food,  always 
involve  a  loss  of  energy. 

The  more  varied  the  enzymes  produced  by  an  organism, 
the  more  varied  may  its  food  be.  For  example,  no  organ- 
ism that  does  not  produce  an  enzyme  that  can  change  gela- 
tin into  soluble  compounds  can  utilize  this  substance  as  food. 
The  classification  and  naming  of  enzymes  is  very  confusing, 
and  need  not  be  introduced  here.  The  enzymes  that  act 
on  protein  are  commonly  called  proteolytic  enzymes.  Some 
can  act  on  a  number  of  different  proteins,  others  on  only  a 
few. 


58  AGRICULTURAL  BACTERIOLOGY 

The  enzymes  are  always  the  product  of  life.  They  seem 
to  stand  between  the  living  and  the  dead,  in  that  they  have 
some  of  the  properties  usually  ascribed  to  life  alone.  They 
are  destroyed  by  heat,  and  are  injured  or  destroyed  by 
those  chemicals  that  have  an  injurious  action  on  the  cell 
itself.  They  are  usually  compared  to  the  inorganic  cata- 
lysts of  the  chemists,  substances  that  favor  in  some  way  a 
chemical  reaction,  and  yet  do  not  enter  directly  into  the 
reaction.  This  comparison  comes  from  the  fact  that  a  mi- 
nute quantity  of  an  enzyme  may  act  on  a  large  amount  of 
material — as,  for  example,  one  part  of  rennet  may  curdle 
one  million  parts  of  milk  in  a  short  time. 

It  is  usually  considered  that  the  unicellular  organism  has 
no  dependence  on  other  cells  of  its  own  kind.  This  is  prob- 
ably not  true.  It  seems  probable  that  the  enzymes  formed 
by  a  cell  do  not  serve  the  originating  cell,  but  a  later  one. 
Many  of  the  enzymes  seem  to  be  set  free  only  on  the  death 
of  the  cell.  If  this  is  true,  the  popular  concept  of  the  in- 
dependent existence  of  a  unicellular  organism  is  not  the 
correct  one  in  all  cases. 

In  a  pure  culture  of  bacteria,  the  dead  cells  undergo  dis- 
solution. Since  there  are  no  outside  sources  for  the  de- 
composing agents,  it  is  clear  that  they  must  come  from  the 
cells  themselves.  Such  decomposition  by  the  inherent  en- 
zymes of  the  cell,  or  mass  of  cells,  is  termed  autolysis.  It  is 
noted  especially  in  the  dissolution  of  bacterial  cells  after 
spores  have  been  formed.  It  is  also  met  in  the  tissues  of 
higher  plants  and  animals. 

The  food  requirements  of  microorganisms  vary  widely. 
Those  that  live  on  dead  organic  matter  are  called  sapro- 
phytic; those  that  grow  in  the  bodies  of  plants  and  animals 
are  termed  parasitic.  Many  of  the  bacteria  that  grow  in 
the  animal  body  are  perfectly  harmless  to  the  host ;  such  are 
called  commensal  organisms.     The  disease-producing  organ- 


PHYSIOLOGY  OF  MICROORGANISMS  59 

isms  are  parasitic.  This  classification  of  the  organisms  as 
they  grow  in  nature  does  not  hold  under  laboratory  condi- 
tions, since  many  of  the  parasitic  bacteria  can  be  grown  on 
dead  matter.  The  parasitic  organisms  find  favorable  con- 
ditions for  growth  in  the  body  of  plant  or  animal.  If  these 
conditions  can  be  duplicated  or  approximated  in  the  labora- 
iory,  the  organism  will  grow  independent  of  the  living 
host. 

The  bacteria  are  of  far  greater  importance  in  causing 
decomposition  than  are  the  yeasts  and  molds.  This  rests 
largely  on  their  cosmopolitan  nature  as  far  as  growth  is  con- 
cerned. They  grow  over  a  wider  range  of  temperature 
than  any  other  group.  They  grow  with  or  without  air,  and 
can  make  use  of  the  most  varied  materials  as  food.  These 
facts,  coupled  with  the  extreme  rapidity  of  growth,  insures 
the,  predominance  of  bacteria  over  other  organisms  when- 
ever the  reaction  or  concentration  of  the  food  material  per- 
mits til  em  to  develop. 

Metabiosis. — Organic  matter  is  decomposed  by  the  agency 
of  all  forms  of  life  that  do  not  use  the  energj^  directly  from 
the  sun.  The  decomposition  is  complete;  each  element  is 
returned  to  that  form  in  which  it  was  when  it  was  utilized 
by  the  green  plant.  No  one  form  is  able  to  cause  the  com- 
plete decomposition  of  a  mixture  of  organic  substances. 
The  process  is  usually  carried  on  by  a  sequence  of  forms, 
the  second  using  the  by-products  of  the  first  as  food  mate- 
rial. The  ])y-products  of  the  second  supply  food  and 
energy  for  a  third,  and  the  process  goes  on,  with  a  gradual 
dissipation  of  energy  and  the  formation  of  more  and  more 
simple  compounds.  This  action  of  a  sequence  of  organisms 
is  termed  metabiosis.  It  is  of  great  importance,  not  only  in 
nature,  but  also  in  the  fermentation  industries. 

The  gradual  degradation  of  organic  matter  by  a  series  of 
organisms  is  usually  known  only  in  part,  either  with  refer- 


60  AGRICULTURAL  BACTERIOLOGY 

ence  to  the  causal  forms  or  to  the  chemical  processes  in- 
volved. In  the  decomposition  of  certain  carbohydrates  the 
process  is  more  simple  and  may  be  followed  in  its  essential 
details.  Starch  may  be  acted  on  by  certain  organisms 
through  their  enzymes,  and  a  complex  sugar  formed,  as 
maltose  (CiaHoaOn).  The  latter,  by  the  same  organism  or 
by  another,  may  be  changed  to  a  simpler  sugar,  glucose 
(CoIIigOc),  which  may  be  fermented  by  yeasts  with  the  for- 
mation of  carbon-dioxide  and  alcohol  (CsHjOII).  The 
former  compound  is  available  for  the  green  plant.  The 
latter  may  be  used  by  certain  bacteria  which  oxidize  it  to 
acetic  acid  (C2H4O2),  which,  in  its  turn,  is  changed  by 
molds  to  carbon-dioxide  and  water.  The  elements  con- 
tained in  the  sugar  are  now  all  available  to  the  green  plant. 
It  is  not  to  be  understood  that  this  is  the  particular  path 
alwa^^s  followed  in  the  decomposition  of  starch.  Innumer- 
able deviations,  both  as  to  organisms  and  products,  may 
occur.  It  is  presented  simply  as  an  example  of  metabiosis. 
The  initial  steps  in  the  process  described  can  be  carried 
out  under  anaerobic  conditions.  The  decomposition  of  acids 
is  a  process  for  which  the  molds  are  especially  fitted.  These 
are  all  aerobic.  Therefore,  if  the  process  is  to  go  on  to  com- 
pletion, aerobic  conditions  must  be  established.  It  may  be 
stated  as  a  general  fact  that  the  initial  processes  in  all  de- 
composition may  take  place  under  anaerobic  conditions,  but 
that  the  final  steps  can  go  on  only  under  aerobic  conditions. 
This  fact,  which  is  of  great  importance  in  many  practical 
relations,  finds  its  explanation  in  that  the  initial  steps  are 
accomplished  largely  by  the  addition  of  water  to  the  mole- 
cules to  be  broken  up.  This  process  is  termed  hydrolysis. 
A  simple  splitting  up  of  the  molecule  may  also  occur.  The 
final  stages  involve  the  addition  of  oxygen  to  the  molecule. 
All  of  these  processes  are  illustrated  in  the  equations  pre- 
sented : 


PHYSIOLOGY  OF  MICROORGANISMS  61 

2  CcHjoOs  +  H.O  =  CJl^jOu 
Starch  -j-  Water  :=  Maltose 
C„HaOa  +  H,0  =  C«H.30e  +  C.H„Oe 
Maltose  -(-  Water  =:  Dextrose  -j-  Dextrose 
CeH,  A  =2  CjU.OH  -f  2  CO, 
Dextrose  =i  Etliyl  Alcohol  -f-  Carbon-dioxide 
CjII.OII  +  Oa  =CJ1A  -f  II2O 
Ethyl  alcohol  -|-  Oxvgen  =  Acetic  acid  -f-  Water 
CJI,0=  +  2  O2  =  2  CO2  +  2  U,0 
Acetic  acid  4-  Oxygen  =:  Carbon-dioxide  -|-  Water 

It  must  not  be  thought  that  these  equations  present  the 
entire  process.  They  simply  present  the  chief  reactions. 
For  example,  the  following  equation,  CoHioOo  =  2  CgH-OH 
+  2  CO2,  implies  that  all  of  the  sugar  appears  as  alcohol 
and  carbon-dioxide.  The  true  reaction  is  more  like  the  fol- 
lowing: Dextrose  +  Yeast  =  Alcohol  +  Carbon-dioxide 
-(-  products  of  unknown  nature  +  yeast  °.  In  other 
words,  a  part  of  the  sugar  is  used  in  the  formation  of 
numerous  products  other  than  the  chief  by-products,  and 
another  part  of  the  sugar  is  used  in  building  the  new  yeast 
cells,  for  decomposition  goes  on  only  as  the  organisms 
proliferate. 

Relation  of  the  organism  to  its  by-products. — It  is  evi- 
dent that,  if  an  organism  changes  sugar  to  carbon-dioxide 
and  water,  it  will  derive  more  energy  from  a  given  amount 
of  sugar  than  will  another  organism  that  forms  an  organic 
acid  from  the  sugar.  The  organic  acid  contains  much 
energy,  while  the  carbon-dioxide  and  water  do  not.  If  the 
two  organisms  are  to  secure  an  equal  amount  of  energy 
from  sugar,  the  second  must  decompose  a  much  greater 
amount  of  sugar  than  the  first.  With  the  organism  that 
causes  complete  decomposition  of  the  sugar  the  amount  of 
by-products  may  not  greatly  exceed  that  of  the  mass  of 
cells  resulting  from  the  decomposition.  In  other  words,  a 
large  part  of  the  food  is  used  for  the  building  of  cells.  This 
is  made  possible  by  the  fact  that  the  organism  uses  all  the 


62  AGRICULTURAL  BACTERIOLOGY 

energy  contained  in  its  food.  In  the  case  of  the  organism 
that  forms  by-products  that  contain  much  energy,  the 
weight  of  the  cells  will  be  insignificant  in  comparison  to 
that  of  the  by-products.  The  first  type  of  organism  will  be 
of  no  value  in  the  manufacture  of  products  of  industrial 
value,  nor  will  it  be  of  importance  in  disease  production, 
except  as  it  may  cause  mechanical  injury.  It  is  this  prop- 
erty of  partial  decomposition  of  their  food  that  gives  to 
the  bacteria  and  the  yeasts  their  great  importance  in  indus- 
trial fermentations,  and  that  makes  the  bacteria  such  potent 
agents  in  the  causation  of  disease.  The  animals  and  the 
strictly  aerobic  forms  of  microorganisms  carry  on  the  de- 
composition of  their  food  to  a  very  complete  degree.  In 
other  words,  their  waste  products  are  simple  in  composition, 
and  contain  little  energy.  It  should  be  kept  in  mind  that 
the  microorganisms  derive  both  building  material  and 
energy  from  their  food.  Certain  constituents  of  the  food 
may  contain  no  energy,  and  can,  of  course,  be  used  only 
for  the  formation  of  the  cell  substance.  Other  foods  may 
serve  both  purposes.  Indeed,  the  greater  part  of  the  food 
will  be  thus  used.  It  is  customary  to  speak  of  food  for 
energy  and  of  food  for  growth. 

Classes  of  organic  matter. — The  greater  part  of  vegetable 
and  animal  matter  is  to  be  included  under  the  following 
great  groups :  carbohydrates,  which  include  the  celluloses, 
the  starches,  and  the  sugars,  compounds  containing  carbon, 
hydrogen,  and  oxygen;  proteins,  which  in  addition  to  the 
above  elements  also  contain  nitrogen,  sulphur,  and  some- 
times phosphorus;  and  the  fats,  which  contain  the  same 
elements  as  the  carbohydrates.  The  latter  are,  however,  less 
easily  decomposed  by  microorganisms  than  are  the  carbo- 
hydrates. The  chemical  transformations  that  these  organic 
compounds  undergo  as  they  are  acted  upon  by  microorgan- 
isms can  be  most  clearly  represented  in  connection  with  the 


DISTRIBUTION  OF  MICROORGANSMS         63 

applied  phases  of  our  subject.  The  cycle  of  each  element 
is  as  important  in  the  economy  of  nature  as  is  that  of  any 
other  element.  The  interest  in  decomposition  processes  is 
chiefly  limited,  however,  to  the  cycles  of  carbon,  nitrogen, 
and  sulphur. 

Distribution  of  microorganisms. — It  is  evident,  from 
what  has  been  said,  that  microorganisms  will  abound  wher- 
ever organic  matter  is  present  and  where  other  conditions 
will  permit  them  to  grow.  The  annual  crop  of  organic  mat- 
ter finds  its  way  to  the  soil,  there  to  be  destroyed  by  the 
microorganisms  and  by  the  lower  forms  of  animal  life. 
Virtually  every  soil  yields  suflficient  vegetation  to  support 
an  abundant  crop  of  microorganisms.  The  soil  is  the  most 
important  of  the  habitats  of  the  bacteria.  In  it  are  found 
the  most  varied  kinds,  both  from  the  standpoint  of  mor- 
phology and  physiology.  The  number,  as  determined  by 
the  plate-culture  method,  ranges  from  a  few  thousand  per 
gram  to  several  million;  but  it  must  be  remembered  that 
the  number  determined  by  the  plate  culture  represents  only 
a  portion  of  the  total  bacterial  flora  of  the  soil.  It  is  cer- 
tain that  each  gram  of  cultivated  soil  contains  hundreds  of 
millions  of  organisms. 

The  number  of  bacteria  in  the  soil  decreases  rapidly  with 
the  depth,  so  that  at  varying  depths  the  soil  ultimately  be- 
comes sterile.  The  decrease  in  bacteria  with  increasing 
depth  is  probably  due  to  a  number  of  factors,  such  as  ab- 
sence of  free  oxygen  and  lack  of  food.  In  the  denser  soils 
the  filtering  action  is  undoubtedly  important.  Liquids  can 
be  sterilized  by  passing  them  through  a  filter  of  unglazed 
porcelain.  The  soil  acts  in  a  similar  manner,  removing 
mechanically  the  bacteria  from  the  water  percolating 
through  it.  The  soil  also  contains  yeasts,  molds,  and  proto- 
zoa in  varying  numbers. 

The  bacterial  content  of  the  ground  water  will  depend  on 


64  AGRICULTURAL  BACTERIOLOGY 

the  depth  of  the  stratum  from  which  it  comes.  That  de- 
rived from  superficial  layers  will  contain  many  bacteria, 
while  that  from  the  deeper  levels  is  free  from  them.  The 
surface  waters  vary  widely  in  bacterial  content,  the  chief 
determining  factors  being  the  amount  of  organic  matter 
that  they  receive  and  the  amount  of  soil  carried  by  the 
water.  The  bacteria  are  found  in  the  greatest  depths  of  the 
ocean  that  have  been  examined. 

Factors  that  keep  the  number  of  bacteria  reduced  are 
operative  in  both  soil  and  water.  The  cycle  of  life  in  water 
is  something  as  follows:  Many  of  the  protozoa  feed  upon 
bacteria;  the  protozoa  in  turn  are  used  as  food  by  the 
Crustacea,  which  make  up  a  large  part  of  the  food  of  many 
fish.  If  it  were  not  for  these  restraining  factors,  many  of 
our  waterways  into  which  sewage  is  discharged  would  be- 
come so  offensive  as  to  cause  a  nuisance. 

Lack  of  food  and  moisture  do  not  permit  the  growth  of 
bacteria  in  the  air.  They  are  found  there,  however,  in 
widely  varying  numbers.  The  soil  is  undoubtedly  the  chief 
point  of  origin.  The  greater  the  dust  content  of  the  air, 
the  greater  will  be  its  content  in  microorganisms.  The  air 
has  a  characteristic  bacterial  flora,  which  consists  of  forms 
that  are  able  to  resist  desiccation. 

The  number  of  dust  particles  in  the  air  is  greater  in  the 
city  than  in  the  open  country.  It  has  been  shown  that 
only  a  few  of  the  dust  particles  carry  bacteria.  The  studies 
of  Whipple  on  the  air  of  school-rooms  showed  an  average 
dust  content  of  871,000  per  cubic  foot,  and  but  113  bacteria 
in  the  same  volume. 

The  tissues  of  healthy  animals  are  free,  or  relatively  free, 
from  bacteria;  but  within  the  alimentary  tract  they  grow 
profusely  at  all  levels,  except  within  the  stomach,  where 
they  are  restrained  by  the  acid  of  the  stomach  juices.  In 
the  intestine  conditions  are  especially  favorable  with  refer- 


DISTRIBUTION  OF  MICROORGANSMS         65 

ence  to  temperature,  moisture,  food,  and  removal  of  by- 
products. The  feces  of  all  animals  are  especially  high  in 
bacteria.  The  bacteria  are  present  in  the  superficial  layers 
of  the  skin. 

The  tissues  of  plants  are  undoubtedly  free  from  bacteria. 
They  are  present  on  the  surface  of  the  leaves  in  such  num- 
bers and  vary  so  much  from  the  normal  soil  flora  that 
it  is  certain  growth  occurs  thereon.  The  occurrence  of 
bacteria  on  plants  has  been  studied  but  little. 


PART  II 
SOIL  BACTERIOLOGY 


CHAPTER  VI 

THE  RELATION  OP  MICROORGANISMS  TO 
SOIL  FERTILITY 

The  basic  work  of  the  farmer  is  the  growing  of  plants  of 
economic  value.  All  other  work  is  incidental  and  insig- 
nificant in  comparison  with  the  throwing  of  the  green  plant 
that  is  to  supply  food  for  man  and  for  the  animals  he  has 
brought  to  his  service.  The  farmer's  primary  interest  is 
therefore  in  the  soil,  as  the  place  in  which  the  plants  he 
desires  to  cultivate  will  grow. 

There  are  many  factors  that  determine  whether  the  soil 
is  a  place  in  which  the  plant  can  grow  well  and  yield  to  the 
farmer  a  large  return  for  his  labor.  The  texture  of  the 
soil  must  be  such  that  the  roots  of  the  plant  can  penetrate 
it  freely,  in  order  that  they  may  draw  food  and  water  from 
a  large  volume  of  the  soil.  The  water  content  of  the  soil 
must  vary  within  certain  limits.  If  it  is  too  low,  the 
growth  of  the  plant  will  be  checked;  if  it  is  too  high,  the 
factors  preparing  the  food  for  the  plant  will  be  interfered 
with,  and  again  growth  will  be  retarded.  The  temperature 
must  be  favorable  for  the  plant,  and  also  for  the  agents  that 
are  active  in  making  the  food  ready  for  it.  Lastly,  there 
must  be  a  supply  of  food  in  fitting  form  for  the  crop.  If 
the  farmer  is  to  be  successful  in  the  highest  sense,  he  must 
control  these  various  factors. 

The  control  can  not  be  absolute,  but  it  may  be  exercised  to 
a  high  degree.  The  farmer  must  have  before  his  eyes  not 
only  the  crop  of  the  year,  but  of  the  next  year,  of  the  next 


70  AGRICULTURAL  BACTERIOLOGY 

decade,  and  of  the  coming  century.  He  must  so  handle  his 
soil  that  it  shall  be  now  and  in  the  future  a  place  in  which 
the  green  plant  will  find  favorable  conditions  for  develop- 
ment. In  the  handling  of  the  soil^  the  farmer  must  con- 
sider the  multitudes  of  microorganisms  that  are  growing 
therein. 

Unavailable  and  available  plant  food.— The  green  plant 
obtains  its  carbon  from  the  carbon-dioxide  of  the  air,  its 
oxygen  from  the  same  source,  its  hydrogen  from  water. 
Nitrogen,  phosphorus,  calcium,  magnesium,  potassium,  sul- 
phur, iron,  and  silicon  must  be  supplied  from  the  soil. 
The  plant  must  be  furnished  with  each  of  these  elements  in 
certain  definite  chemical  compounds.  One  property  that 
all  these  compounds  must  possess  is  solubility  in  water. 
The  food  must  pass  into  the  roots  through  the  firm  cell  wall 
by  the  process  of  osmosis. 

The  great  agricultural  districts  of  the  world  are  in  the 
humid  regions,  where  the  rainfall  is  sufficient  to  allow  the 
larger  part  of  the  water  to  pass  through  the  soil  until  it 
reaches  the  so-called  ground-water  layer.  The  water,  as  it 
passes  downward,  tends  to  dissolve  and  transport  with  it  all 
soluble  soil  constituents.  The  storage  of  plant  food  in  a 
form  available  to  the  plant  is  incompatible  with  this  condi- 
tion. The  food  must  be  stored  in  an  insoluble  form,  and 
thus  be  protected  from  the  leaching  action  of  water.  This 
available  food  must  be  prepared  for  use  by  the  plant 
through  the  action  of  some  slowly  acting  factors,  such  as  the 
solvent  effect  of  water  on  materials  that  are  ordinarily 
classed  as  insoluble.  Weathering,  the  mechanical  reduction 
in  size  of  soil  particles  under  the  action  of  frost,  and  the 
effect  of  biochemical  agents  such  as  bacterial  activity,  are 
factors  that  release  plant  food  for  use  by  the  green  plant. 

The  fertility  of  any  soil  depends  upon  the  amount  of  un- 
available plant  food  stored  therein,  upon  its  potential  fer- 


MICROORGANISMS  AND  SOIL  FERTILITY      71 

tility,  and  upon  the  rate  at  which  the  chemical,  physical, 
and  biological  factors  are  preparing  it  for  the  green  plant. 
Of  these  the  biological  factors  are  tlie  most  important.  The 
various  kinds  of  microorganisms  feed  upon  the  organic 
matter,  changing  it  into  simpler  compounds,  until  the  vari- 
ous elements  are  in  a  form  usable  by  the  green  plant.  At 
the  beginning  of  each  growing  season  there  is  a  minimum  of 
available  plant  food ;  hence  the  unavailable  reserve  must  be 
changed  into  an  available  supply.  This  means  that  the 
farmer  must  grow  a  crop  of  microorganisms  to  prepare  the 
way  for  the  visible  crop.  The  supply  of  food  for  his  field 
crop,  and  therefore  the  yield  of  the  same,  depends  in  no 
small  degree  on  the  success  with  which  he  grows  his  micro- 
scopic crop. 

In  the  newer  portions  of  the  world,  the  farmer  pays  little 
attention  to  any  other  source  of  plant  food  than  the  soil. 
In  the  older  agricultural  regions,  the  store  of  plant  food 
has  been  partially  exhausted.  The  plant  must  grow  on  the 
material  the  farmer  adds  to  the  soil  in  the  form  of  organic 
matter.  Under  these  conditions,  the  chief  interest  is  in 
the  efficiency  of  the  soil  organisms,  and  in  their  ability  to 
transform  the  added  potential  plant  food  to  the  available 
food  supply. 

From  this  point  of  view  the  soil  becomes  a  factory  where 
multitudes  of  workers  are  working  over  the  raw  material, 
converting  it  into  the  finished  food  for  the  green  plant. 
The  soil  must  therefore  be  favorable  for  the  growth  of  the 
microorganisms  that  are  concerned  in  the  cycles  of  carbon, 
nitrogen,  sulphur,  and  phosphorus,  the  four  main  elements 
the  plant  derives  from  the  soil.  The  lack  of  any  one  of 
these  elements  in  compounds  available  to  the  plant  will 
limit  the  growth  of  the  crop.  Nitrogen  is  most  often  the 
element  that  acts  as  a  limiting  factor  to  the  development  of 
the  plant ;  for,  in  the  final  form  in  which  it  appears  in  the 


72  AGRICULTURAL  BACTERIOLOGY 

decomposition  of  organic  matter,  nitrates,  it  is  easily  leached 
from  the  soil. 

The  soil  as  a  culture  medium. — The  amount  and  kind  of 
bacterial  growth  in  the  soil,  and  therefore  the  quantity  of 
food  available  to  the  green  plant,  will  depend  on  many  fac- 
tors. The  chief  factor  is  the  food  supply.  If  large  amounts 
of  organic  matter  are  added  to  the  soil,  as  will  be  the  case 
under  natural  conditions  where  the  entire  crop  is  returned 
to  it,  the  amount  of  food  will  be  large.  If  the  crop  is  re- 
moved and  sold  in  its  entirety,  as  in  the  case  in  grass  farm- 
ing, the  amount  of  organic  matter  returned  to  the  soil  will 
be  reduced  to  a  minimum.  Again,  a  farmer  may  purchase 
feed,  hay,  and  grain  for  the  use  of  his  animals,  and  by  add- 
ing the  manure  produced  to  his  fields,  he  increases  the  food 
supply  of  the  bacteria  in  the  soil.  In  market-gardening 
the  addition,  in  the  form  of  manure  from  the  cities,  of  many 
tons  of  organic  matter  grown  on  the  soil  of  distant  farms 
permits  a  large  development  of  bacteria,  and  therefore  an 
increased  crop  of  vegetables.  Without  a  beginning  there 
can  be  no  end ;  without  bacterial  food  in  the  soil  there  can 
be  no  food  crop  for  man  or  beast. 

Moisture  and  air. — The  amount  of  water  in  the  soil  has 
an  influence  not  only  on  the  total  amount  of  bacterial 
growth,  but  also  on  the  types  of  organisms  that  may  grow — 
a  factor  of  great  importance  in  determining  the  kinds  of 
green  plants  that  may  develop  in  any  soil. 

The  soil  is  a  porous  structure  made  up  of  minerals  in 
varying  states  of  subdivision.  The  interspaces  in  the  soil 
may  be  completely  filled  with  water,  as  in  a  water-logged 
soil.  Under  such  conditions  only  facultative  and  anaerobic 
organisms  can  grow.  If  the  soil  spaces  are  filled  with  air, 
aerobic  as  well  as  facultative  bacteria  can  develop.  The 
so-called  hydrostatic  water  is  removed  from  the  soil  by 
gravity.     It  tends  to  carry  with  it  the  soluble  constituents 


MICROORGANISMS  AND  SOIL  FERTILITY      73 

of  the  soil.  Evaporation  of  moisture  is  constantly  taking 
place  at  the  surface.  To  replace  this  loss  by  evaporation, 
through  capillary  action  of  the  soil  particles,  the  water 
moves  upward  toward  the  surface.  Ultimately  a  point  is 
reached  at  which  the  water  films  surrounding  the  soil  par- 
ticles become  so  thin  that  this  upward  movement  does  not 
continue  to  replace  the  loss  due  to  evaporation.  Such  a 
soil  is  said  to  be  air-dry,  and  contains  only  hygroscopic 
moisture.  It  is  doubtful  whether  bacteria  can  grow  in  such 
a  soil.  It  is  probable  that  the  soil  of  humid  regions  never 
becomes  so  dry  as  to  destroy  any  large  portion  of  the  non- 
spore-forming  bacteria  by  desiccation. 

In  coarse-grained  soils  the  extent  of  surface  of  the  parti- 
cles in  a  unit  volume  of  the  soil  is  much  less  than  in  a  finer 
soil.  It  is  thus  evident  that  in  a  fine  soil  a  given  amount 
of  water  will  form  a  thinner  film,  and  be  more  tightly  held 
by  the  soil  particles,  than  will  be  the  case  with  a  coarse  soil. 
A  state  of  physiological  dryness  will  therefore  be  reached 
at  a  higher  water  content  in  fine  soil  than  in  a  coarse  soil. 

The  air  supply  of  the  soil  is  in  an  inverse  ratio  to  its 
water  content.  As  the  water  is  removed  by  drainage  or 
evaporation,  the  pore  spaces  become  filled  with  air.  In 
coarse  sandy  soils  the  air  supply  is  usually  sufficient  to  favor 
rapid  bacterial  action.  Indeed,  often  the  farmer  is  de- 
sirous of  limiting  the  air  supply  by  packing  and  rolling  the 
soil  in  order  to  retard  decomposition.  The  ventilation  of 
close-textured  soils,  owing  to  variations  in  atmospheric  pres- 
sure and  to  the  eff^'ect  of  wind,  is  not  sufficient  to  cause  any 
rapid  replacement  of  the  soil  air  laden  with  carbon-dioxide 
by  atmospheric  air.  Under  the  most  favorable  natural  con- 
ditions, the  aeration  of  such  soils  is  insufficient  to  permit 
the  rapid  growth  of  such  pronounced  aerobic  organisms  as 
the  nitrifying  bacteria,  except  at  the  immediate  surface. 
In  the  close-textured  soils  the  decomposition  of  organic  mat- 


74  AGRICULTURAL  BACTERIOLOGY 

ter  is  slow  and  often  incomplete.  Here  the  efforts  of  the 
farmer  must  be  directed  toward  more  perfect  aeration.  All 
processes  of  cultivation  aid,  as  does  drainage. 

Temperature. — The  temperature  zone  in  which  bacterial 
growth  is  possible  is  a  wide  one,  extending  from  below 
0°  to  70°  C.  (32°-158°  F.).  Representatives  of  both  psy- 
chrophilic  and  thermophilic  bacteria  are  found  in  the  soil. 
The  great  mass  of  bacteria  in  the  soil  are  mesophilic,  and 
are  favored  by  relatively  high  temperatures,  from  16°  to 
40°  C.  (61°-104°  F.).  It  is  customary  to  speak  of  cold 
or  late  soils,  and  of  warm  or  early  soils.  The  former  are 
those  of  close  texture,  which  in  the  spring  become  dry 
enough  to  cultivate  only  after  a  considerable  period. 
Water  has  a  high  specific  heat.  A  soil  filled  with  water  will 
therefore  increase  in  temperature  slowly  as  compared  with 
one  containing  a  smaller  amount  of  moisture.  The  time 
required  for  the  temperature  of  the  soil  to  reach  a  point  at 
which  bacterial  growth  will  be  rapid  will  be  prolonged  in  a 
close  soil.  The  supply  of  available  plant  food  is  largely 
removed  from  the  soil  by  the  percolating  water  of  fall,  win- 
ter, and  spring.  Before  the  crop  can  make  any  marked 
growth,  opportunity  must  be  afforded  for  the  soil  organisms 
to  form  available  plant  food.  This  process  will  be  retarded 
in  a  wet  soil,  hence  the  expression  "late  soil."  The  loss  of 
water  and  decomposition  of  organic  matter  take  place 
quickly  in  open-textured  soils.  The  expression  "early 
soils"  is  therefore  a  fitting  one  to  apply  to  them.  The 
gardener  needs  a  loose,  sandy  soil  for  his  early  crops. 

Reaction  of  the  soil. — The  bacteria  are  favored  by  a  neu- 
tral or  slightly  alkaline  rather  than  by  an  acid  reaction. 
An  acid  reaction  in  the  food  medium  is  not  injurious  to 
yeasts  and  molds.  The  greater  part  of  the  elaboration  of 
plant  food  from  organic  matter  in  the  soil  is  occasioned  by 


MICROORGANISMS  AND  SOIL  FERTILITY      75 

bacteria.  It  is,  therefore,  essential  that  the  soils  in  which 
the  acid  reaction  is  pronounced  be  neutralized  by  the  addi- 
tion of  lime,  in  order  that  the  decomposition  of  the  organic 
matter  be  favored,  and  hence  conditions  established  for  a 
luxuriant  growth  of  the  seeded  crop. 

The  decomposition  of  organic  matter  under  anaerobic  con- 
ditions is  incomplete;  acids  persist — thus  marsh  lands  are 
often  acid  in  reaction.  By  drainage  of  such  lands,  air  is 
admitted  and  the  growth  of  molds  is  made  possible.  These 
organisms  will  gradually  destroy  the  acids,  and  the  reaction 
of  the  soil  will  be  changed  in  time  so  as  to  be  more  favor- 
able for  bacterial  action  and  for  plant  growth.  Drainage 
and  cultivation  may  soon  make  a  marsh  soil  a  fitting  place 
for  plants  tliat  are  very  susceptible  to  acid. 

Number  of  organisms  in  soil. — The  number  of  bacteria 
in  a  soil,  as  has  been  shown,  is  dependent  on  many  factors, 
chief  among  which  is  the  amount  of  organic  matter.  The 
bacterial  content  of  a  sandy  soil  may  be  but  a  few  hundred 
thousand  per  gram,  that  of  a  rich  garden  soil  several  mil- 
lion per  gram.  The  bacterial  content  of  soil  is  determined 
by  the  plate-culture  method,  using  some  particular  kind  of 
culture  medium.  It  should  be  understood  that  only  a  por- 
tion, probably  a  very  small  portion,  of  the  total  bacterial 
flora  of  the  soil  is  thus  revealed;  for  only  the  bacteria  that 
can  grow  on  the  medium  used,  and  at  the  temperature  and 
in  the  oxygen  tension  at  which  the  cultures  are  kept,  can 
develop.  It  seems  probable  that,  in  any  soil  that  will  per- 
mit the  growth  of  higher  plants,  the  bacteria  are  to  be  meas- 
ured by  the  hundreds  of  millions  per  gram.  The  higher  the 
fertility  of  the  soil,  the  higher  will  be  its  bacterial  content ; 
for  the  bacteria  are  the  direct  cause  of  the  former,  through 
their  elaboration  of  plant  food. 

The  soil  also  contains  many  molds  and  yeasts.     Little  is 


76  AGRICULTURAL  BACTERIOLOGY 

known  of  the  effect  they  produce  in  the  soil.  They  are, 
however,  to  be  considered  as  agents  in  the  decomposition  of 
organic  matter  and  in  the  elaboration  of  plant  food. 

Protozoa,  unicellular  animals,  are  present  in  the  soil  in 
numbers  reaching  several  thousand  per  gram.  It  is  to  be 
remembered  that  every  animal  is  a  factor  in  the  decompo- 
sition of  organic  matter.  The  relatively  large  size  of  the 
protozoa  makes  them  an  appreciable  factor  in  the  elabora- 
tion of  plant  food.  Many  protozoa  live  on  bacteria,  and  it 
has  been  claimed  by  some  students  of  the  soil  that  they  are 
the  cause  of  the  reduced  fertility  of  many  soils,  since  they 
cause  the  destruction  of  certain  classes  of  bacteria  that  are 
essential  in  the  cycle  of  nitrogen.  It  is  a  well  known  fact 
that  the  bacterial  content  of  surface  waters  is  kept  at  a  low 
level  by  the  protozoa. 

The  macroscopic  lower  animal  forms  in  and  on  the  soil 
are  likewise  abundant  and  also  function  in  the  decompo- 
sition of  organic  matter.  It  has  been  shown  that  from  ten 
to  fifteen  million  insects  of  macroscopic  size  may  be  found 
on  a  single  acre  of  meadow-land.  Within  the  soil  the  com- 
mon earthworm  occurs  in  varying  numbers.  Determina- 
tions indicate  that  as  high  as  350  pounds  per  acre  of  these 
organisms  may  be  found  in  the  more  fertile  soils.  All  of 
these  forms  are  living  on  complex,  organic  compounds,  and 
are  giving  off  simple  waste  products.  They  also  function 
in  the  pulverization  of  organic  matter,  and  thus  make  it 
more  easily  attacked  by  microorganisms.  The  earthworm 
is  also  of  importance  in  the  aeration  of  the  soil  through  its 
burrows.  The  soil  is  passed  through  the  alimentary  tract 
of  the  earthworm,  and  is  brought  by  them  to  the  surface 
in  their  "castings."  This  reworking  of  the  soil  particles 
materially  improves  the  texture  of  the  soil.  When  land  is 
plowed  that  has  been  under  grass  for  a  number  of  years,  it 
will  be  found  to  possess  a  granular  structure,  due  to  the 


MICROORGANISMS  AND  SOIL  FERTILITY      77 

action  of  earthworms  and  the  roots  of  the  higher  plants. 
The  ordinary  concept  of  the  soil,  that  it  is  an  inert  mass 
of  mineral  matter,  is  therefore  far  from  the  fact.  It  is 
filled  with  the  most  varied  kinds  of  living  things  of  micro- 
scopic size,  the  work  of  which  is  as  vital  to  animal  existence 
as  it  is  to  the  green  plant.  The  farmer  must  care  for  these 
tiny  inhabitants  of  the  soil  as  well  as  for  his  crops  and 
animals. 


CHAPTER  VII 

THE  DECOMPOSITION  OF  ORGANIC  MATTER 
IN  THE  SOIL 

Almost  every  conceivable  organic  compound  is  added  to 
the  soil  in  the  plant  and  animal  matter  that  finds  its  way 
therein.  All  is  grist  for  the  mill  of  the  microorganisms  of 
the  soil.  So  far  as  is  known,  no  substance  is  able  to  resist 
their  action ;  even  such  resistant  substances  as  chitin,  horn, 
and  gums  ultimately  disappear,  as  do  the  bones  of  animals 
that  are  placed  in  the  upper  layers  of  the  soil.  If,  in  some 
way,  they  have  been  deposited  in  the  lower  layers  of  the 
earth  or  in  a  place  where  they  are  protected  from  the  action 
of  microorganisms,  they  will  persist  for  ages. 

From  the  standpoint  of  the  action  of  the  decomposing 
matter  6n  the  fertility  of  the  soil  and  from  the  viewpoint 
of  the  farmer,  all  organic  matter  may  be  divided  into  two 
great  groups :  first,  those  compounds  that  contain  only  car- 
bon, hydrogen,  and  oxygen,  of  which  the  sugars  and  starches 
are  examples;  second,  the  nitrogen-containing  substances 
that  are  best  illustrated  by  the  proteins.  These  latter  com- 
pounds also  contain  sulphur  and  phosphorus,  the  cycles  of 
which  are  of  interest  to  the  farmer. 

The  decomposition  of  all  of  these  substances,  with  the 
formation  of  those  compounds  in  which  the  various  ele- 
ments are  available  to  the  green  plant,  is  an  intricate  proc- 
ess from  the  standpoint  of  the  chemical  reactions  concerned 
and  the  organisms  involved.  Knowledge  of  the  complete 
process  is  yet  fragmentary  and  incomplete.  Only  a  few 
general  facts  are  known,  and  little  of  the  details  of  the 

78 


DECOMPOSITION  IN  THE  SOIL  79 

gradual  degradation  of  organic  matter  hy  microorganisms. 

No  single  form  can  act  on  an  organic  compound  and 
change  it  into  the  final  products  of  decomposition.  ^lany 
forms  are  concerned  in  the  complete  decomposition  of  the 
simplest  forms  of  organic  matter.  The  various  organisms 
concerned  may  bear  different  relations  to  one  another.  The 
most  common  and  the  most  important  of  these  relations  is 
that  already  discussed,  to  which  tbe  term  metabiosis  is  ap- 
plied. It  is  to  be  noted,  from  the  example  of  metabiosis 
given  on  page  59,  that  the  processes  of  hydration  are  first 
involved,  later  dextrose  is  split  into  alcohol  and  carbon- 
dioxide,  and  this  is  followed  by  oxidation.  The  former 
processes  can  take  place  in  the  absence  of  free  oxygen 
under  the  influence  of  facultative  organisms.  The  com- 
pletion of  the  decomposition  process  must  be  occasioned  by 
aerobic  forms.  This  fact  is  noted  also  in  the  decomposition 
of  all  organic  matter;  the  final  stages  are  always  due  to 
aerobic  organisms.  This  fact  implies  the  accumulation  of 
partially  decomposed  organic  matter  under  conditions 
where  oxygen  is  not  abundant,  a  phenomenon  of  the  utmost 
importance  in  the  soil. 

The  degradation  of  starch  does  not  always  occur  on  the 
lines  laid  down ;  from  sugar,  acids  rather  than  alcohol  may 
be  formed.  Lactic,  acetic,  formic,  butj^ic,  and  propionic 
acids  are  the  most  common.  The  formation  of  acids  from 
sugar  and  alcohol  is  chiefly  due  to  bacteria,  while  yeasts  are 
the  prime  factors  in  the  production  of  alcohol. 

It  is  to  be  noted  that,  in  the  decomposition  of  carbohy- 
drates, acids  of  varying  strength  are  formed,  down  to  the 
weak  carbonic  acid.  This  accounts  for  the  acid  reaction  in 
decomposing  organic  matter  in  which  carbohydrates  pre- 
dominate over  proteins,  which  in  their  decomposition  yield 
ammonia.  The  reaction  of  decomposing  protein  will  be 
alkaline,   as  exemplified  in  eggs   and   meats.     It  may  be 


80  AGRICULTURAL  BACTERIOLOGY 

stated  as  a  general  truth  that,  in  material  consisting  of  a 
mixture  of  sugars  and  proteins,  the  former  will  be  the  first 
to  be  attacked  in  processes  of  decomposition,  with  the  result 
that  an  acid  reaction  will  be  established  which  will  prevent 
further  decomposition,  except  as  it  may  be  occasioned  by 
such  organisms  as  the  molds  which  use  acid  as  food.  If 
any  condition,  such  as  the  absence  of  free  oxygen,  does  not 
permit  these  aerobic  forms  to  grow,  the  partially  decom- 
posed material  will  not  suffer  further  action.  This  fact  is 
of  great  practical  importance  in  the  soil. 

In  the  decomposition  of  organic  matter  under  the  action 
of  a  sequence  of  forms,  each  of  which  obtains  its  building 
material  and  its  energy  from  the  food  consumed,  the  mater- 
ial is  gradually  changed  to  a  more  stable  form  and  its  energy 
content  reduced  until  it  reaches  a  stage  in  which  the  vari- 
ous elements  are  available  for  the  use  of  the  green  plant. 

Humus. — The  soil  was  originally  formed  from  the  disin- 
tegration of  the  rocks,  and  at  first  contained  no  organic 
matter.  In  the  evolution  of  life,  plants  began  to  grow  in 
the  soil.  Following  their  death,  decay  occurred.  If  the 
decomposition  had  been  complete,  the  soil  would  have  re- 
mained purely  inorganic  matter,  since  the  final  products  of 
decomposition  are  readily  soluble  in  water.  If  decompo- 
sition is  not  complete,  a  residue  of  partially  decomposed 
organic  matter  remains  in  or  on  the  ground.  To  this  resi- 
due the  term  humus  is  applied.  The  content  of  the  soil  in 
humus  varies  from  an  almost  complete  absence  to  soils  in 
which  it  is  the  most  prominent  constituent.  The  accumu- 
lation of  humus  is  exceedingly  slow.  It  has  required  many 
thousand  years  to  accumulate  the  amount  found  in  rich 
prairie  soils.  Under  cultivation  it  is  removed  at  an  infin- 
itely more  rapid  rate  than  it  was  formed. 

The  rate  and  extent  at  which  humus  accumulates  bears 


DECOMPOSITION  IN  THE  SOIL  81 

an  intimate  relation  to  the  aeration  of  the  soil,  and  the  op- 
portunity for  the  growth  of  the  aerol)i('  orj^anisms  that  are 
the  most  prominent  agents  in  the  final  decomposition  of 
organic  matter.  In  marsh  soils  the  accumulation  of  humus 
is  great,  due  to  the  water-logged  condition.  The  opposite 
extreme  is  noted  in  the  coarse,  sandy  soils  in  which  the  air 
supply  is  at  a  maximum.  Neither  of  these  soils  represents 
the  highest  type  of  fertility.  Marsh  soils  are  low  in  fertil- 
ity, because  the  kind  of  compounds  demanded  by  the  most 
important  cultivated  crops  have  not  been  formed  therein. 
Sands  are  relatively  infertile,  because  no  store  of  new  plant 
food  is  accumulated.  The  maximum  of  fertility  is  attained 
in  the  loam  soils,  which  contain  enough  oxygen  to  enable  a 
portion  of  the  organic  matter  to  be  completely  decomposed, 
and  yet  permit  of  the  gradual  accumulation  of  humus. 

All  types  of  soils  are  much  better  aerated  under  cultiva- 
tion than  under  natural  conditions.  The  result  is  that  the 
store  of  humus  is  gradually  reduced  and  the  fertility  of  the 
soil  is  diminished.  The  humus  aft'ects  the  fertility  not  only 
by  forming  a  store  of  plant  food,  but  by  its  effect  on  the 
water-holding  capacity  of  the  soil  and  on  its  texture.  If  the 
farmer  does  not  return  to  the  soil  most  of  the  organic  mat- 
ter it  has  produced,  soil  exhaustion  is  inevitable. 

The  maintenance  of  the  humus  content  of  the  soil  is  one 
of  the  important  problems  of  the  farmer  in  the  older 
regions  of  the  world.  The  type  of  farming  has  much  influ- 
ence on  this.  If  grass-growing  is  the  chief  industry,  no  or- 
ganic matter  is  returned  to  the  soil  and  the  humus 
content  will  be  constantly  depleted.  The  same  is  true  of 
grain-farming  when  no  effort  is  made  to  return  the  straw  to 
the  soil,  as  is  the  case  in  the  grain-growing  sections  of  this 
country  where  the  straw  is  burned.  If  the  farm  crops  are 
fed  to  animals,  and  what  they  produce  is  sold  in  the  form 


82  AGRICULTURAL  BACTERIOLOGY 

of  dairy  products,  live  stock,  wool,  and  the  like,  while  the 
manure  is  returned  to  the  land,  the  tendency  will  be  to 
maintain  the  humus  content  of  the  soil. 

The  crop  grown  on  most  cultivated  lands  is  larger  than 
the  land  would  produce  under  natural  conditions.  In  other 
words  man  by  his  tillage  operations  establishes  more  favor- 
able conditions  for  the  action  of  microorganisms  in  the  soil 
than  obtains  in  nature.  This  results  in  the  more  rapid 
change  of  the  unavailable  to  available  plant  food,  a  process 
that  hastens  the  reduction  of  the  humus  content. 

The  difference  in  the  rate  and  completeness  of  the  decom- 
position of  organic  matter  in  the  various  types  of  soils  is 
shown  when  manure  is  added  to  them.  An  application  of 
barnyard  manure  to  a  sandy  field  may  show  its  effect  in  an 
increased  crop  only  during  the  season  in  which  it  was  ap- 
plied, while  in  the  case  of  a  clay  soil  its  effect  may  be  noted 
for  two  or  three  years.  Again,  when  it  is  desired  to  use 
land  for  the  disposal  of  organic  matter,  as  in  the  case  of 
sewage,  the  best  conditions  are  found  in  an  open,  sandy 
soil,  in  which  the  process  will  go  on  rapidly  and  completely 
with  little  or  no  accumulation  of  humus.  In  denser  soils, 
a  much  larger  area  is  required,  as  the  applications  can  be 
made  with  less  frequency,  or  the  soil  becomes  clogged  with 
the  accumulation  of  organic  matter  which  can  not  be  decom- 
posed by  reason  of  the  lack  of  growth  of  aerobic  organisms. 
The  disposal  of  sewage  by  conducting  it  on  to  the  land  is 
used  only  when  areas  of  sandy  land  are  available. 


CHAPTER  VIII 
THE  CYCLE  OP  CARBON 

The  cycle  of  carbon  may  be  best  presented  in  the  decom- 
position of  the  carboliydrates.  The  carbon  in  fats  and  in 
proteins  is  ultimately  changed  into  the  same  form  as  in 
carbohydrates,  e.  g.  carbon-dioxide.  ^lany  of  the  decom- 
positions of  carbohydrates  are  of  industrial  importance  and 
will  be  discussed  later.  Others  can  most  conveniently  be 
considered  in  connection  with  the  soil  processes. 

During  the  growing  season,  the  green  plants  draw  heavily 
on  the  carbon-dioxide  in  the  air.  It  is,  of  course,  clear 
that,  if  agencies  are  not  operating  to  return  the  carbon  to 
the  air  as  carbon-dioxide,  the  growth  of  green  plants  will 
ultimately  be  limited.  The  air  contains  from  0.03  to  0.04 
per  cent,  of  carbon-dioxide. 

Every  living  form  produces  carbon-dioxide  through  its 
respiratory  processes.  The  green  plant  during  daylight 
hours  is  both  producing  and  consuming  this  gas;  the  former 
is  accomplished  in  respiration,  the  latter  by  photosynthesis. 
The  two  processes  tend  to  balance  each  other.  In  the  dark 
photosynthesis  is  stopped,  while  carbon-dioxide  production 
goes  on.  All  animals  and  fungus  plants  produce  carbon- 
dioxide.  The  green  plant  robs  the  air  of  its  carbon-dioxide ; 
the  rest  of  living  things  replace  it,  and  thus  life  is  able  to 
continue  its  round.  The  decomposition  of  organic  matter 
taking  place  in  the  soil  abstracts  oxygen  from  the  soil 
air,  and  increases  its  content  in  carbon-dioxide,  until  as 
much  as  from  2  to  9  per  cent,  of  this  gas  may  be  found  in 
the  soil.     Poor  ventilation  of  the  soil  tends  to  maintain  the 

83 


84  AGRICULTURAL  BACTERIOLOGY 

carbon-dioxide  therein.  This  is  dissolved  in  the  soil  water, 
thereby  increasing  materially  its  solvent  effect  on  certain 
of  the  minerals  of  the  soil. 

Organic  acids  are  always  produced  in  the  decomposition 
of  carbohydrates.  In  poorly  aerated  soils  these  tend  to 
accumulate,  forming  the  raw  or  acid  humus  noted  in  marshy 
soils.  Hydrogen  and  also  methane  may  be  formed.  The 
latter  is  commonly  called  marsh-gas,  from  its  formation  in 
water-logged  areas  by  anaerobic  and  facultative  bacteria. 

Cellulose  decomposition. — The  decomposition  of  certain 
carbohydrates  is  of  special  importance  to  the  farmer.  The 
great  mass  of  plant  tissue  consists  largely  of  cellulose,  a  com- 
pound that  is  insoluble  in  water  and  resistant  to  decompo- 
sition. The  plant  fibers,  such  as  cotton  and  hemp  which  are 
used  for  industrial  purposes,  consist  of  cellulose.  The 
larger  portion  of  organic  matter  in  barnyard  manure  also 
consists  of  cellulose.  It  is  believed  that  cellulose  is  acted 
on  by  microorganisms  with  the  formation  of  sugars,  as  in 
the  case  of  starch.  In  the  soil  these  are  at  once  changed  to 
still  simpler  compounds. 

Quantities  of  cellulose  are  contained  in  the  rough  feed, 
hay  and  grass,  consumed  by  animals.  It  has  been  found 
that  ruminants  can  digest  about  75  per  cent,  of  the  cellulose 
contained  in  the  feed;  horses  about  50  per  cent.,  man  about 
25  per  cent,  of  that  contained  in  young,  tender  plants,  while 
the  dog  can  not  digest  cellulose  at  all.  As  has  been  previ- 
ously stated,  all  insoluble  foods  ingested  by  the  animal  are 
supposed  to  be  changed  to  soluble  compounds  by  the  action 
of  enzymes  elaborated  by  the  animal  body.  No  enzyme 
capable  of  acting  in  cellulose  has,  as  yet,  been  demonstrated 
in  the  animal  bod}^  The  only  explanation  that  can  be 
offered  is  that  bacteria,  which  change  the  cellulose  to  sugars, 
are  present  in  the  alimentary  tracts  of  animals  and  that 
these  sugars  are  utilized  by  the  animal. 


CYCLE  OF  CARBON  85 

The  animals  that  can  digest  eellulose  most  completely  are 
those  ill  which  the  food  is  retaiiied  in  the  body  for  a  long 
period  of  time.  In  the  case  of  the  cow  and  the  sheep  this 
extends  to  six  or  seven  days.  In  the  laboratory  the  decom- 
position of  cellulose  is  slow,  but  the  conditions  are  not  so 
favorable  as  in  the  animal,  where  the  temperature  and 
moisture  conditions  are  at  the  optimum;  the  constant  re- 
moval of  the  by-products  is  again  of  the  utmost  importance 
in  determining  the  rate  at  which  any  biological  process  will 
be  maintained. 

Whether  this  is  the  only  service  to  the  animal  that  is 
rendered  by  the  immense  numbers  of  microorganisms  grow- 
ing in  the  intestinal  tract  of  animals  ma^-  be  doubted. 
.Many  experiments  have  been  made  in  the  hope  of  deter- 
mining whether  the  life  of  the  higher  animals  would  be  pos- 
sible without  the  presence  of  bacteria  in  the  alimentary 
tract.  It  is  very  difficult  to  maintain  an  animal  in  a  per- 
fectly sterile  condition  and  still  keep  it  otherwise  normal. 
The  general  conclusion  to  be  drawn  from  such  experiments 
as  have  been  most  successful  is  that,  while  the  bacteria  ma}' 
not  be  necessary  for  the  life  of  the  higher  animals,  they  are 
of  great  importance  in  aiding  the  animal  to  utilize  its  food, 
and  that  probably  such  action  is  not  confined  to  the  cel- 
luloses. The  relation  existing  between  the  animal  and  the 
bacteria  of  the  intestinal  tract  is  one  in  which  the  animal 
is  deriving  some  benefit.  There  is  a  more  or  less  character- 
istic flora  for  each  kind  of  animal.  If  this  flora  is  replaced 
by  an  abnormal  one,  the  helpful  relation  may  be  changed 
to  one  in  which  the  animal  is  injured.  It  is  believed  that 
the  condition  known  as  autointoxication  in  man  is  due  to 
the  replacement  of  the  normal  acid-producing  flora  by  one 
that  acts  primarily  on  proteins,  with  the  production  of 
poisonous  substances  that  are  absorbed  from  the  alimentary 
tract  and  exert  a  cumulative  effect  on  the  animal.     Metchni- 


86  AGRICULTURAL  BACTERIOLOGY 

koff,  the  Russian  bacteriologist,  also  asserts  that  what  are 
usually  regarded  as  symptoms  of  old  age  in  man  are  due  to 
the  gradual  replacement  of  the  normal  flora  by  a  harmful 
one. 

Retting  of  fiber  plants. — In  the  preparation  of  the  fibers 
from  such  plants  as  hemp  and  flax,  it  is  necessary  to  decom- 
pose the  binding  substances  that  hold  the  fibers  together. 
These  bodies  a.re  carbohydrates  and  are  known  as  pectins. 
In  the  rotting  or  "retting"  process,  it  is  essential  that  the 
cellulose  fibers  shall  not  be  acted  on  so  as  to  weaken  their 
strength.  In  the  case  of  flax,  the  straw  may  be  immersed 
in  water  for  a  short  time,  or  it  may  be  allowed  to  lie  on  the 
surface  of  the  ground.  The  bacteria  and  molds  quickly  de- 
compose the  pectins,  and  by  breaking  the  straw  into  short 
pieces  the  fil)er  may  then  be  freed  from  the  binding  mater- 
ial. In  some  parts  of  the  world  certain  streams  have  been 
found  to  be  very  favorable  for  the  retting  of  flax.  The  river 
Lys  in  Belgium  is  a  famous  place  for  flax  retting.  The 
content  of  the  water  in  pectin-decomposing  organisms  is  sup- 
posed to  be  the  explanation  of  the  favorable  action  of  this 
river.  Efforts  have  been  made  to  isolate  pure  cultures  of 
the  pectin-fermenting  organisms,  and  to  use  them  in  the 
retting  of  flax  in  tanks,  instead  of  exposing  it  in  natural 
waters.  Pectin-decomposing  organisms  play  an  important 
role  in  the  spoiling  of  fruits  and  vegetables. 

Oxidation  of  hydrogen  and  methane. — Hydrogen  and 
methane  are  commonly  formed  in  the  decomposition  of  car- 
bohydrates. Neither  the  hydrogen  nor  the  carbon  is  here 
available  for  the  green  plant.  Bacteria  have  been  found 
that  are  able  to  oxidize  such  energy-containing  gases,  form- 
ing the  ultimate  decomposition  products,  carbon-dioxide 
and  water. 


CHAPTER  IX 

THE  ACTION  OF  BACTERIA  ON  THE  MINERALS  OF 
THE  SOIL 

The  mineral  portion  of  the  soil  consists  almost  wholly  of 
carbonates,  sulphates,  phosphates,  chlorides,  and  silicates, 
which  are,  of  course,  relatively  insoluble,  otherwise  they 
would  be  removed  by  the  percolating  water.  The  water 
that  falls  on  the  soil  in  the  form  of  rain  contains  no  mineral 
matter,  or  at  most  only  traces;  but  drainage  or  well  water 
contains  considerable  quantities  of  mineral  matter  in  solu- 
tion. It  is  thus  apparent  that  processes  are  at  work  in  the 
soil  by  which  some  of  the  minerals  of  the  soil  are  being  con- 
verted into  soluble  compounds.  In  all  ground  waters  will  be 
found  carbonates,  sulphates,  nitrates,  and  chlorides  of  cal- 
cium, magnesium,  potassium  and  sodium. 

Probably  none  of  the  minerals  of  the  soil  is  absolutely 
insoluble  in  pure  water,  but  most  of  them  are  so  slightly  af- 
fected by  the  water  as  to  be  classed  as  insoluble.  As  has 
been  shown,  various  organic  acids  are  formed  in  the  decom- 
position of  organic  matter.  A  strong  acid,  nitric  acid,  is 
also  the  final  product  in  the  decomposition  of  nitrogenous 
compounds.  Ultimately  all  the  carbon  of  organic  matter 
appears  as  carbonic  acid.  These  various  acids  are  dissolved 
in  the  soil  water,  and  influence  its  action  on  the  minerals 
of  the  soil,  which  by  their  fine  state  of  division  present  an 
enormous  surface  to  it. 

Calcium. — The  limestone  that  is  found  in  the  soil  was  re- 
moved from  the  water  of  the  sea  by  the  action  of  the  shell- 
forming  animals.     At  the  death  of  the  animal  the  shell 

87 


88 


AGRICULTURAL  BACTERIOLOGY 


was  deposited  on  the  floor  of  the  sea,  and  in  time  limestone 
deposits  were  produced.  By  some  movement  of  the  earth's 
crust  the  floor  of  the  sea  was  lifted  above  the  water-level  and 


Fig.  20.     Etching  of  Marble  by  Plant  TlooU 

The   picture  on   the   left  shows  the  solvent  action   of   plant  roots   on    a  marble 

slab  in  the  absence  of  bacteria;  the  one  on  the  right  the  action  in  the  presence 

of  bacteria.      The  latter  have  formed  acids  from  the   material  given   off  by  the 

plant  and  have  increased  the  solvent  action  on  the  calcium  carbonate 

After  Fred. 

subjected  to  weathering.  These  deposits  were  also  ground 
by  the  action  of  the  ice  in  the  great  glaciers  that  swept  over  a 
large  part  of  the  country,  or  they  were  disintegrated  by  the 
weather,  so  that  a  great  mass  of  limestone  found  its  way  into 
the  soil. 

The  carbon-dioxide  dissolved  in  the  soil  water  increases 
the  solvent  action  of  the  water  on  the  calc^ium  carbonate, 


ACTION  ON  MINERALS  89 

bringing  it  into  solution  in  the  form  of  calcium  bicarbonate, 
which  is  removed  in  the  drainage  water.  Thus  ultimately 
all  of  the  limestone  that  was  formed  in  the  sea  is  returned 
to  it,  largely  by  virtue  of  tlie  indirect  action  of  soil  organ- 
isms. It  is  estimated  that  lime  is  being  removed  from  our 
soils  at  the  rate  of  from  400  to  1,000  pounds  an  acre  each 
year.  The  increased  amount  of  decomposition  of  organic 
matter  due  to  cultivation  of  the  soil  hastens  the  removal 
of  the  limestone  therefrom.  Ultimately  the  lime  is  removed 
to  such  an  extent  that  the  soils  tend  to  become  acid,  and 
limestone  must  be  added.  This  again  favors  decomposition 
of  the  organic  matter,  and  the  removal  of  the  lime  is  has- 
tened. 

It  is  improbable  that  the  organic  acidi^  hasten  to  a  great 
extent  the  removal  of  calcium  carbonate  from  the  soil. 
It  is  true  that  they  will  act  on  this  mineral:  salts  of  the 
respective  acids  which  are  soluble  in  water  will  be  formed. 
The  acid  radicle  of  these  salts  will  be  decomposed  and 
carbon-dioxide  will  be  produced,  which  will  combine  with 
the  calcium  to  form  calcium  carbonate  again.  The  cal- 
cium nitrate  formed  in  the  soil  may  be  leached  therefrom. 
In  the  ocean  this  salt  is  decomposed  by  certain  bacteria, 
forming  therefrom  gaseous  nitrogen  and  calcium  carbonate. 

It  is  probably  true  that  the  calcium  contained  in  organic 
matter  appears  as  calcium  carbonate  at  the  end  of  the  de- 
composition process.  The  amount  thus  formed  is  but  a 
small  fraction  of  that  removed  from  the  soil. 

Lime  is  added  to  the  soil  in  the  form  of  ground  limestone 
(carbonate  of  calcium,  marl)  or  burned  lime  (calcium 
oxide).  It  is  essential  that  lime  be  in  as  fine  a  state  of 
division  as  possible,  so  that  it  can  be  mixed  thoroughly 
with  the  soil  and  be  brought  in  intimate  contact  with  each 
soil  grain. 

Phosphorus. — Phosphorus    is    another    element    that    is 


90  AGRICULTURAL  BACTERIOLOGY 

needed  by  the  growing  plant,  and  is  often  found  in  such 
small  amounts  in  an  available  form  as  to  limit  the  yield  of 
the  crop.  It  occurs  in  the  soil  in  the  form  of  calcium 
phosphate,  iron,  and  aluminum  phosphate,  and  in  organic 
matter.     All  these  forms  are  insoluble  in  water. 

In  the  Southern  States  there  are  great  deposits  of  cal- 
cium phosphate,  or  rock  phosphate  as  it  is  often  called. 
This  rock  is  ground  to  a  very  fine  powder  which  is  sold 
under  the  name  floats.  This  source  of  phosphatic  fertil- 
izer is  the  most  important  one.  Superphosphate,  which 
represents  a  more  soluble  form  of  phosphate,  is  often  used. 
It  is  produced  bj^  treating  the  ground-rock  phosphate  with 
sulphuric  acid,  forming  the  acid  phosphate.  Phosphoric 
acid  contains  three  atoms  of  hydrogen  that  can  be  replaced 
by  such  a  base  as  calcium.  The  acid  phosphates  that  are 
obtained  when  but  one  or  two  of  the  hydrogen  atoms  are 
replaced  by  calcium  are  soluble  in  water,  while  the  normal 
phosphate  is  not.  Superphosphate  is  added  when  a  quick 
acting  phosphatic  fertilizer  is  desired. 

If  the  insoluble  phosphates  in  the  soil  are  to  be  made 
available  to  the  green  plant,  they  must  be  rendered  soluble 
by  processes  similar  to  those  used  by  the  manufacturer  of 
superphosphate.  The  acids  to  accomplish  the  change  must 
be  those  formed  in  the  decomposition  of  the  organic  matter 
added  to  the  soil.  It  is  generally  recommended  that 
ground-rock  phosphate  be  mixed  with  barnyard  manure, 
or  that  it  be  applied  directly  to  the  land  when  the  green 
manuring  process  is  to  be  tried.  It  would  be  useless  to 
add  rock  phosphate  to  a  light  sandy  soil  that  is  quite  devoid 
of  organic  matter.  The  phosphorus  in  organic  matter  be- 
comes available  to  the  green  plant  on  the  decomposition  of 
the  material.  The  various  chemical  changes  through 
which  it  passes  are  not  known. 

Potassium. — Potassium  is  found  in  the  soil  largely  in 


ACTION  ON  MINERALS  91 

the  form  of  an  insoluble  silicate,  which  also  contains  alum- 
inum. A  soil  may  contain  thousands  of  pounds  of  this 
potassium  compound  to  an  acre  and  yet  may  respond  to 
the  application  of  solul)le  potassium  salts.  It  is  believed 
that  the  by-products  of  bacterial  action  have  an  effect 
upon  the  insoluble  compounds,  tending  to  bring  some  of 
the  potassium  into  soluble  form.  For  example,  the  bicar- 
bonate of  lime  is  supposed  to  react  with  the  aluminum- 
potassium  salt,  forming  potassium  bicarbonate.  It  is 
probable  that  stronger  organic  acids  formed  in  the  decom- 
position of  organic  matter  exert  a  solvent  action  on  the 
potassium  compounds  of  the  soil. 

It  is  essential  to  have  soluble  potassium  compounds  not 
only  for  the  green  plants  but  for  some  of  the  important 
classes  of  bacteria  in  the  soil. 

Sulphur. — Sulphur  is  an  essential  constituent  of  every 
plant  or  animal  cell.  The  green  plants  derive  their  sup- 
ply from  the  sulphates  of  the  soil.  The  amount  of  sulphur 
needed  is  so  small  that  in  most  soils  there  is  an  abundant 
supply  for  the  needs  of  the  crop.  Some  soils,  however,  re- 
spond to  the  application  of  sulphur.  It  is  probable  that 
the  favorable  action  of  superphosphate  is  sometimes  due 
to  the  sulphur  it  contains. 

The  sulphur  of  organic  matter  appears  as  a  sulphide 
when  the  material  undergoes  decomposition.  When  the 
decomposing  material  is  high  in  sulphur,  as  in  the  case  of 
the  egg:,  the  odor  of  this  gas  is  very  apparent.  The  odor 
may  also  be  noticeable  in  sewage,  in  which  the  formation 
of  hydrogen  sulphide  can  be  easily  shown  by  adding  a 
little  ferrous  sulphate.  The  iron  is  precipitated  as  iron 
sulphide,  which  is  black  in  color. 

Hydrogen  sulphide  contains  much  energy  and  forms  a 
source  from  which  certain  bacteria  derive  the  energy  for 
growth.     They  oxidize  the  sulphide  to  free  sulphur,  which 


92  AGRICULTURAL  BACTERIOLOGY 

may  be  stored  in  their  cells  to  be  further  oxidized  to  siil- 
I)hurie  acid,  which  will  combine  with  bases  to  form  sul- 
phates, producing  compounds  in  which  the  sulphur  is  avail- 
able to  the  green  plant.  Such  bacteria  are  found  in  the 
soil,  and  in  great  abundance  in  sulphur  springs.  Their 
action  results  in  the  formation  of  a  strong  mineral  acid, 
which  exerts  a  solvent  action  on  many  of  the  soil  minerals. 
Sulphur  is  lost  in  the  drainage  water  in  the  form  of  sul- 
phates. 

The  reduction  of  sulphates  by  bacteria  is  a  common  pro- 
cess when  sea  water  is  mixed  with  water  carrying  organic 
matter.  Such  conditions  occur  when  sewage  is  discharged 
into  tidal  rivers.  The  dissolved  oxygen  of  the  water  is 
soon  exhausted  by  the  bacteria  feeding  on  the  organic 
matter.  The  facultative  bacteria  must  utilize  some  other 
source  of  oxygen,  and  find  a  supply  in  the  sulphates,  which 
are  thus  reduced  to  sulphides.  This  process  may  be  so 
pronounced  as  to  create  a  nuisance  in  cities  located  on  the 
sea. 

Iron. — Iron  is  often  present  in  ground  water  as  ferrous 
carbonate.  Certain  bacteria  known  as  the  iron  bacteria 
facilitate  the  precipitation  of  the  iron  from  the  water. 
The  insoluble  iron  accumulates  in  the  sheaths  of  the  bac- 
teria, among  which  many  of  the  higher  bacteria  are  to  be 
noted.  Some  of  the  iron  bacteria  have  peculiar  forms,  such 
as  flat,  twisted  ribbons. 

It  is  believed  that  they  have  been  the  causal  agents  in 
the  deposition  of  many  of  the  great  iron-ore  deposits  such 
as  are  found  in  northern  Minnesota.  They  often  cause 
the  accumulation  of  a  deposit  on  the  inside  of  water- 
mains  through  which  an  iron-bearing  water  passes.  They 
also  may  cause  the  plugging  of  drain-tile  in  marshy  land. 
The  acids  produced  from  the  decomposition  of  organic 
matter  dissolve  the  iron,  which  is  carried  by  the  percolat- 


ACTION  ON  MINERALS  93 

ing  water  into  the  drains,  there  to  be  precipitated.     These 
bacteria  are  often  to  be  noted  in  masses  in  iron  springs. 

It  is  quite  probable  that  the  soil  bacteria  influence  the 
tilth  of  the  soil;  that  they  influence  the  loss  of  moisture 
from  it ;  and  that  they  are  the  cause  of  the  earthy  odor  that 
is  so  characteristic.  This  is  due  to  volatile  substances 
formed  in  the  decomposition  of  the  organic  matter  in  the 
soil. 


CHAPTER  X 
THE  CYCLE  OF  NITROGEN 

While  it  is  perhaps  impossible  to  characterize  any  one 
process  as  more  essential  than  some  other,  where  all  are 
necessary  steps  in  a  complex  relationship,  it  is  undoubt- 
edly true  that  the  cycle  which  nitrogen  undergoes  in  nature 
is  invested  with  the  greatest  interest  of  any  of  the  ele- 
ments, because  of  the  intricacy  of  the  changes  involved, 
their  dependence  on  one  another,  the  completeness  with 
which  the  various  steps  have  been  traced,  and  the  possi- 
bility of  controlling  by  scientific  knowledge  the  progress 
of  these  changes. 

Nitrogen  is  constantly  being  removed  from  the  soil  by 
growing  plants,  and  it  is  essential  that  in  some  manner  the 
nitrogen  be  returned  to  the  soil  and  again  made  available 
to  the  plant.  In  the  discussion  of  the  cycle  of  carbon  it 
was  shown  that  not  only  were  microorganisms  instrumen- 
tal in  the  return  of  the  carbon  of  organic  matter  to  a  form 
in  which  the  plant  can  again  make  use  of  it,  but  that  both 
animals  and  plants  are  giving  off  carbon-dioxide  as  a  pro- 
duct of  their  respiration.  In  the  case  of  nitrogen  it  will 
be  seen  that  microorganisms  are  the  only  agents  by  which 
the  nitrogen  in  plant  and  animal  matter  can  be  made 
available  to  the  green  plant. 

The  amount  of  free  nitrogen  in  the  world  is  enormous. 
The  air  contains  80  per  cent,  of  this  element.  Over  every 
acre  there  are  35,000  tons  of  this  gas.  Nitrogen  is  an  inert 
element  anci  does  not  readily  enter  into  combination  with 
other  elements,  such  as  the  oxygen  of  the  air ;  but  there  are 

94 


CYCLE  OF  NITROGEN  95 

both  chemical  and  biological  methods  of  bringing  nitrogen 
into  combination.  The  difficulty  of  brin2:ing  about  these 
reactions  is  indicated  by  the  fact  that,  in  spite  of  the 
immense  amount  of  free  nitrogen,  combined  nitrogen,  un- 
der existing  commercial  conditions,  costs  considerably  more 
than  any  other  food  element. 

The  nitrogen  of  the  soil.— The  store  of  nitrogen  in  the 
soil  is  in  the  humus,  the  residue  of  the  organic  matter  that 
has  undergone  decomposition  in  the  soil.  The  content  of 
average  arable  soils  in  nitrogen  is  from  0.1  to  0.2  per  cent., 
but  the  nitrogen  in  humus  is  not  available  to  the  plant, 
because  the  humus  is  insoluble.  It  is  a  very  fortunate  pro- 
vision of  nature  that  a  portion  of  the  nitrogen  that  has 
been  added  to  the  soil  in  the  organic  matter  has  been 
thus  stored.  If  it  were  all  immediately  available,  that 
which  was  not  used  by  the  growing  plant  would  be  quickly 
leached  from  the  soil  in  the  drainage  water. 

Under  natural  conditions,  some  nitrogen  is  lost  in  the 
drainage  water.  As  will  be  seen  later,  factors  are  operat- 
ing in  every  soil  by  which  combined  nitrogen  is  added  to 
it.  Where  the  entire  crop  is  returned  to  the  land,  as  is 
true  under  uncultivated  conditions,  the  nitrogen  content 
of  most  soils  slowly  increases.  Thus  has  accumulated 
through  many  thousands  of  years  the  present  nitrogen  sup- 
ply of  our  soils.  Under  cultivation,  the  removal  of  the 
crop  and  the  loss  by  leaching  more  than  balance  the  gain, 
and  the  soil  becomes  depleted  of  nitrogen.  There  comes  a 
time  when  nitrogenous  fertilizers  must  be  added  to  main- 
tain the  crop-producing  power.  This  addition  may  be 
made  in  a  variety  of  ways.  Besides  the  plant  residues, 
animal  material  maj^  be  purchased,  such  as  blood  and  bone 
meal,  fish  scrap,  wool  waste,  etc.  Guano,  the  excrement 
of  birds,  originallj^  formed  an  important  source  of  nitro- 
genous fertilizers.     Besides  natural  plant  and  animal  ma- 


96  AGRICULTURAL  BACTERIOLOGY 

terial,  ammonium  sulphate  and  sodium  nitrate  are  used  as 
fertilizers. 

It  is  probable  that  plants  can  make  use  of  nitrogen  in 
a  number  of  different  compounds,  varying  with  the  kind 
of  plant.  Some  plants,  as  potatoes  and  rice,  can  use  am- 
moniacal  nitrogen;  oats  make  use  of  either  ammoniacal 
or  nitrate  nitrogen,  showing  no  preference  for  either; 
while  corn  and  beets  must  have  their-  nitrogen  needs 
supplied  in  the  form  of  nitrates.  Most  of  our  culti- 
vated plants  demand  all  or  a  portion  of  their  nitrogen  in 
the  form  of  nitrates,  and  can  make  a  normal  growth  only 
in  their  presence.  It  is  thus  essential  that  the  nitrogen 
added  to  the  soil  be  changed  from  protein  nitrogen  to  ni- 
trate nitrogen  before  it  can  be  generally  available.  This 
process  can  be  effected  only  by  the  action  of  the  micro- 
organisms of  the  soil. 

Ammonification. — This  term  is  applied  to  that  portion 
of  the  cycle  of  nitrogen  in  which  protein  nitrogen  is 
changed  to  ammonia.  The  proteins  are  very  complex  sub- 
stances of  high  molecular  weight.  Legumin,  the  charac- 
teristic protein  of  leguminous  plants,  has  been  held  to  have 
the  following  formula:  C7i8Hii5802,8Noi4S,.  The  path 
from  this  complex  molecule  to  carbon-dioxide,  water,  hy- 
drogen sulphide,  and  ammonia  is  a  long  and  largely  un- 
known one,  both  chemically  and  biologically. 

The  organisms  that  use  the  native  proteins  as  food  must 
form  proteolytic  enzymes  which  will  change  the  protein 
into  more  soluble  and  diffusible  compounds  that  can  pass 
into  the  cells.  The  intermediate  products  are  divided  into 
three  great  classes,  the  proteoses,  the  peptones,  and  the 
amino  acids,  the  simplest  of  which  is  glycocoU  or  amino- 
acetic  acid,  having  the  formula  CH.CNHJCOOH.  From 
such  compounds  ammonia  is  easily  formed. 

A  great  number  of  molds  and  bacteria,  aerobic,  faculta- 


AMMONIPICATION  97 

tive,  and  anaerobic,  can  form  ammonia  from  protein.  The 
process  can  thus  go  on  in  the  most  open  soils,  and  also  in 
those  that  are  constantly  saturated  with  water.  The  con- 
ditions that  favor  the  process  are  those  that  favor  bacterial 
growth  in  general,  a  temperature  from  20  °  to  40  °  C, 
(68  °-104  °  F.),  an  abundant  air  supply,  and  a  neutral  re- 
action. 

The  rapidity  with  which  the  process  proceeds  is  largely 
dependent  on  the  material  undergoing  decomposition. 
Some  nitrogenous  fertilizers  are  quickly  ammoniKed,  as 
dried  blood,  ground  fish,  and  tankage;  while  cotton-seed 
meal  and  leather  wastes  are  very  resistant  to  decomposi- 
tion. A  material  resistant  to  decomposition  can  not  be 
used  with  success  as  a  source  of  nitrogen  for  a  quickly 
maturing  crop. 

The  importance  of  ammonification  is  seen  when  it  is  re- 
membered that  every  atom  of  nitrogen  built  into  the  tis- 
sues of  the  green  plant  must  be  converted  into  ammonia 
before  it  can  again  be  used  by  the  plant,  either  as  ammonia 
or  as  nitrate  nitrogen.  Since  the  process  of  ammonifica- 
tion is  an  essential  step  in  the  cycle  of  nitrogen,  it  is  neces- 
sary that  it  go  on  at  such  a  rate  that  the  plant  crop  will  not 
be  limited  by  the  lack  of  nitrogen  in  an  available  form. 
The  establishment  of  a  neutral  reaction  by  the  addition  of 
lime,  the  aeration  of  the  soil  by  the  removal  of  water  by 
drainage  and  by  cultivation,  are  conditions  that  favor  the 
process  of  ammonification.  One  of  the  theories  of  dimin- 
ished soil  fertility  seeks  to  account  for  reduced  yields  by 
the  destruction  of  the  ammonifying  bacteria  by  the  pro- 
tozoa in  the  soil.  The  partial  sterilization  of  soil  by  heat 
or  by  volatile  antiseptics,  such  as  carbon-disulphide,  often 
results  in  an  increased  plant  growth.  It  has  been  believed 
by  some  that  in  such  treatment  of  the  soil  the  protozoa  were 
destroyed,  while  the  development  of  the  ammonifying  bac^ 


98  AGRICULTURAL  BACTERIOLOGY 

teria  went  on  unrestrained;  hence  a  greater  amount  of 
nitrogen  became  available  for  the  crop. 

The  nitrogen  that  has  been  built  into  the  tissues  of  the 
animal  body  is  broken  down  into  simpler  compounds  as  a 
result  of  the  metabolic  activities  of  animals.  The  nitrogen 
waste  from  animals  is  eliminated  in  the  urine  in  the  form 
of  urea,  hippuric  acid,  and  uric  acid.  The  amount  and 
relative  proportions  of  these  three  compounds  vary  in 
the  different  animals.  It  is  estimated  that  60  per  cent,  of 
the  nitrogen  of  the  food  is  eliminated  by  the  horse  in  urine, 
42  per  cent,  in  the  case  of  sheep,  and  31  per  cent,  in  cat- 
tle. In  all  cases  the  nitrogen  in  the  three  compounds  men- 
tioned is  changed  into  ammonia  by  means  of  a  group  of 
bacteria  that  are  most  often  termed  the  urea- fermenting 
organisms.  They  differ  widely  in  their  form  and  struc- 
ture, but  all  have  the  common  property  of  forming  an 
enzyme,  called  urease,  which  changes  the  urea  to  ammon- 
ium carbonate.  This  group  is  found  in  the  soil  and  in 
the  solid  excrement  of  animals.  The  mixing  of  the  solid 
and  liquid  excrement  results  in  the  rapid  change  of  the 
urea  and  allied  compounds  to  ammonia.  The  strong  odor 
of  ammonia  often  noticed  in  horse  stalls  is  due  to  the  fer- 
mentation of  the  urea. 

The  urea-fermenting  bacteria  require  oxygen  for  their 
growth.  They  are  also  favored  by  a  strong  alkaline  reac- 
tion, and  are  able  to  continue  growth  in  the  presence  of 
quantities  of  ammonia  that  would  quickly  stop  the  growth 
of  the  common  putrefactive  bacteria.  The  urine  of  herbi- 
vorous animals  is  alkaline  in  reaction,  while  that  of  man 
and  the  carnivorous  animals  is  acid.  The  former  is  a 
better  medium  for  growth  of  the  urea-fermenting  organ- 
isms. Uric  acid  is  changed  directly  to  ammonium  carbon- 
ate or  to  urea  and  then  to  ammonia.  Hippuric  acid  is 
likewise  fermented  with  the  formation  of  ammonium  car- 


NITRIFICATION  99 

bonate,  or  first  may  be  changed  to  benzoic  acid  and  glyco- 
coll.  The  latter  is  then  ammonified.  The  ease  with  which 
the  ammonification  of  the  nitrogenous  bodies  in  urine  takes 
place  accounts  for  their  high  availability  as  nitrogenous 
fertilizers. 

Nitrification. — While  some  of  the  plants  having  eco- 
nomic value  can  make  use  of  ammonia,  others  can  not,  and 
it  is  necessary  to  have  the  ammonia  oxidized  to  nitric  acid. 
This  process  can  be  accomplished  by  purely  chemical 
means.  Many  porous  substances  have  the  property  of  oc- 
cluding gases  or  of  condensing  them.  The  modification  of 
{Jlatinum  known  as  spongy  platinum  has  this  property  in  a 
high  degree.  If  ammonia  is  brought  in  contact  with  spongy 
platinum,  it  will  be  oxidized  to  nitric  acid. 

Before  anything  was  known  of  the  activity  of  bacteria 
in  such  processes,  it  was  thought  that  the  soil  represented 
such  a  porous  medium.  This  view  was  strengthened  by  the 
manner  in  which  nitrates  were  made  in  earlier  times. 
Large  amounts  were  needed  for  the  gunpowder  used  in  the 
almost  unceasing  war  operations.  The  natural  deposits 
then  known  were  insufficient  for  these  purposes,  hence  the 
necessity  of  manufacturing  nitrates  arose.  This  was  ac- 
complished by  mixing  organic  matter  with  earth.  The  mix- 
ture was  piled  about  brushwood,  which  served  to  make  the 
pile  more  porous.  The  pile  was  kept  moist,  and  a  neutral 
reaction  maintained  by  the  addition  of  limestone  to  the 
mixture  of  soil  and  organic  matter.  After  a  period  the  pile 
was  leached  with  water,  and  the  nitrates  that  had  in  some 
manner  been  formed  were  recovered.  These  piles  were 
known  as  saltpeter  plantations.  The  calcium  or  sodium 
nitrate  thus  obtained  could  be  changed  to  potassium  nitrate 
by  treatment  with  the  lye  leached  from  wood  ashes.  Un- 
til the  discovery  of  the  great  deposits  of  sodium  nitrate  in 
C'hile,  the  larger  part  of  the  nitrates  used  in  the  industries 


100  AGRICULTURAL  BACTERIOLOGY 

were  thus  prepared.  The  Chinese  are  still  using  the  pro- 
cess. Nitrates  can  also  be  obtained  by  the  leaching  of  the 
soil  to  which  large  quantities  of  organic  matter  have  been 
added  and  which  has  been  protected  from  leaching.  Dur- 
ing the  Civil  War  the  Confederate  States  were  forced  to 
leach  the  soil  beneath  old  tobacco  barns.  The  Chinese  re- 
move the  dirt  floors  from  their  houses  and  dissolve  the  ni- 
trate that  has  there  accumulated. 

Many  of  the  characteristics  of  the  change  of  ammonia 
to  nitric  acid  in  the  soil  related  the  process  to  a  biological 
cause.  The  causal  bacteria  were  isolated  by  Winogradsky 
in  1889.  He  confirmed  earlier  observations  that  the  change 
of  ammonia  to  nitric  acid  is  not  a  single  chemical  change, 
but  involves  two  steps:  the  ammonia  is  first  oxidized  to 
nitrous  acid,  and  this  substance  further  oxidized  to  nitric 
acid.  Winogradsky  isolated  two  groups  of  bacteria  con- 
cerned in  these  changes.  The  first  could  grow  only  when 
ammonia  was  available  to  it.  This  compound  represented 
the  sole  source  of  energy  and  of  nitrogen  for  the  organism. 
The  second  group  was  limited  to  the  nitrous  acid  formed  by 
the  first  for  its  energy  and  nitrogen.  The  change  of  am- 
monia to  nitric  acid  is  an  example  of  metabiosis.  The  acids 
formed,  of  course,  unite  with  bases  to  form  neutral  salts, 
nitrites,  and  nitrates. 

The  nitrous  acid-forming  bacteria  difl'er  in  their  mor- 
phology in  various  parts  of  the  world,  but  apparently  all  are 
invested  with  the  same  peculiar  physiological  characteris- 
tics. Earlier  it  was  thought  that  the  presence  of  chlorophyl 
was  essential  for  the  use  of  carbon-dioxide  as  a  source  of 
carbon,  and  that  no  other  type  of  life  than  the  green  plant 
was  able  to  utilize  so  stable  a  substance  as  carbon-dioxide. 
The  nitrifying  bacteria  are  able  to  grow  in  the  total  absence 
of  carbon,  except  in  the  form  of  carbon-dioxide.  Wino- 
gradsky showed  that  the  energy  needed  for  the  process  is 


NITRIFICATION 


101 


i  - 
it 


Fig.  21.     Effect  of  Nitrifying  Bacteria  on  the  Growth  of  Barley 

In  the  absence  of  nitrogen  in  the  soil  the  growth  of  the  plant  has  been  small. 
The  addition  of  sulphate  of  ammonia  has  resulted  in  a  far  better  growth.  Tlie 
addition  of  the  same  substance  and  of  nitrifying  bacteria  that  change  the 
ammoniacal  nitrogen  to  nitric  nitrogen  has  enabled  the  plant  to  make  a 
normal  growth 

After  Fred. 


102  AGRICULTURAL  BACTERIOLOGY 

obtained  through  the  oxidation  of  ammonia  or  nitrous  acid, 
depending  on  the  group  of  nitrifying  bacteria  concerned. 
The  nutrient  solution  must  contain  the  potassium,  sulphur, 
and  phosphorus  needed  for  the  structure  of  the  bacteria, 
but  these  may  be  present  in  inorganic  form.  The  am- 
monia in  the  soil  or  in  the  nutrient  solution  may  be  in  the 
form  of  a  neutral  .  salt,  such  as  ammonium  sulphate. 
Through  the  activity  of  the  bacteria,  an  alkaline-reacting 
radicle,  ammonium,  is  changed  to  an  acid — nitrous  acid. 
This,  together  with  the  sulphate  radicle,  causes  the  rapid 
increase  of  acidity  in  the  soil  or  in  the  solution  in  which 
the  first  step  in  nitrification  is  going  on.  It  is  essential  to 
have  a  neutralizing  agent  present,  such  as  calcium  carbon- 
ate, else  the  process  will  soon  stop.  An  abundant  supply 
of  oxygen  is  also  essential,  as  it  is  for  all  oxidizing  pro- 
cesses. The  organisms  grow  best  at  about  30  °  to  35  °  C, 
(86°-95°F,). 

Nitrification  in  the  soil. — If  nitrification  is  to  go  on  rap- 
idly in  the  soil,  conditions  that  will  permit  the  rapid  growth 
of  the  causal  bacteria  must  be  established.  One  of  the 
most  important  conditions  is  a  well  aerated  soil.  If  the 
pores  are  filled  with  water,  anaerobic  conditions  prevail  and 
no  nitrification  can  go  on.  In  those  soils  that  naturally  are 
well  drained,  as  sandy  soils,  or  in  which  the  excess  of  water 
is  removed  by  drainage  or  otherwise,  the  air  supply  will 
be  greater,  and  other  conditions  being  equal,  the  oxidation 
of  the  ammonia  formed  by  the  ammonifying  bacteria  will 
go  on  quickly.  It  is  difficult  to  establish  the  most  favor- 
able condition  with  reference  to  oxygen  in  our  soils.  Only 
by  frequent  cultivation  can  the  nitrifying  process  be  kept 
at  its  maximum.  The  formation  of  nitrates  is  most  rapid 
in  the  soil  on  which  a  cultivated  crop  is  growing,  such  as 
com  or  roots.  This  accounts,  in  part  at  least,  for  the 
large  amount  of  dry  matter  these  crops  will  produce  per 


NITRIFICATION  103 

acre.  In  the  making  of  composts  the  frequent  stirring  of 
the  pile  favors  the  process  of  ammouification,  and  of  nitri- 
fication especially. 

Nitrification  goes  on  very  slowly  in  acid  soils,  such  as 
marsh  or  peat  soils.  If  these  are  treated  with  lime  in  such 
quantities  as  to  establish  an  alkaline  reaction,  the  formation 
of  nitrates  will  be  greatly  increased.  In  water-logged  soils 
the  decomposition  of  the  organic  matter  is  incomplete,  and 
the  acid  produced  accumulates.  The  removal  of  the  water 
by  drainage  permits  the  air  to  enter,  and  thus  gives  oppor- 
tunity for  the  growth  of  aerobic  microorganisms,  such  as 
molds,  that  will  decompose  the  acids,  making  the  soil  a  bet- 
ter home  for  the  nitrifying  bacteria. 

The  nitrification  process  goes  on  slowly  at  low  tempera- 
tures. It  is  probable  that  it  continues  as  long  as  the  soil  is 
not  frozen. 

Conservation  of  nitrogen. — When  moisture  and  tempera- 
ture conditions  are  most  favorable  for  crop  production,  the 
yield  is  often  limited  by  the  lack  of  sufficient  quantities  of 
some  one  element.  Generally  speaking,  this  limiting  ele- 
ment is  most  often  nitrogen.  It  is  again  probable  that  the 
ammonia  is  oxidized  as  rapidly  as  it  is  formed,  but  not 
sufficient  ammonia  is  formed  for  the  needs  of  the  crop.  As 
has  been  indicated,  the  process  of  ammouification  is  favored 
by  the  same  conditions  as  are  known  to  favor  the  process 
of  nitrification.  The  plant  leads  a  sort  of  hand-to-mouth 
existence,  as  far  as  the  supply  of  nitrates  is  concerned,  since 
in  the  growing  season  the  nitrates  are  used  as  fast  as  they 
are  formed.  After  the  crop  is  removed  the  process  of  de- 
composition continues,  and  the  nitrates  accumulate  in  the 
soil,  to  be  removed  in  the  wet  periods  of  the  fall,  winter 
and  spring. 

Since  nitrogen  is  most  frequently  the  element  limiting 
the  growth  of  the  crop,  and  since  the  store  of  nitrogen  in 


104  AGRICULTURAL  BACTERIOLOGY 

the  soil  is  none  too  large,  it  is  essential  that  the  farmer 
use  every  means  to  conserve  the  nitrogen  supply  of  the 
soil.  Much  can  be  done  in  this  regard  by  keeping  a  crop 
on  the  land  constantly.  For  example,  after  the  removal 
of  corn  the  land  may  be  planted  to  rye,  which  will  use  up 
the  nitrates  in  the  soil.  If  this  crop  is  plowed  under  in  the 
spring,  the  organic  matter  will  decompose,  and  the  nitro- 
gen be  made  available  for  the  coming  crop.  It  has  been 
determined  that  four  times  as  much  nitrogen  is  lost  in  the 
drainage  water  as  is  removed  in  the  crop.  This  loss  is  par- 
ticularly heavy  in  the  South,  where  the  long  exposure  of 
the  soil  to  the  winter  rains  gives  a  most  favorable  oppor- 
tunity for  leaching. 

The  fallow  method  of  handling  the  soil  results  in  the  es- 
tablishment of  favorable  conditions  for  decomposition,  be- 
cause of  the  well  aerated  condition  of  the  soil  and  the  re- 
tention of  moisture  in  the  summer  months.  Plant  food 
thus  accumulates  in  the  form  of  nitrates,  so  that  when  a 
crop  of  winter  wheat  or  rye  is  sown  in  the  fall,  rapid 
growth  occurs. 

Nitrate  deposits. — Almost  all  of  the  nitrate  used  in  the 
industries  and  as  a  fertilizer  is  obtained  from  natural  de- 
posits in  Chile.  It  is  believed  that  the  deposits  are  due  to 
the  accumulation  of  large  amounts  of  organic  matter  in 
some  arm  of  the  sea.  This  was  raised  above  sea-level,  and 
underwent  decomposition  in  a  region  in  which  the  rainfall 
was  not  sufficient  to  leach  the  nitrate  into  the  deeper  levels 
of  the  soil,  so  it  accumulated  in  some  such  manner  as  it 
is  now  accumulating  in  some  parts  of  the  West.  In  sections 
of  Colorado  the  nitrate  content  of  orchards  and  of  fields 
has  become  so  high  as  to  destroy  all  vegetation. 

Denitrification. — Nitrogen  is  removed  from  the  reach  of 
green  plants  by  both  chemical  and  biological  processes. 
For  example,  in  the  discharge  of  explosives  of  all  kinds, 


DENITRIFICATION  105 

which  contain  as  a  rule  great  amounts  of  nitrogen,  this  gas 
is  set  free.  The  nitrates  in  the  soil  may  be  destroyed  by 
bacteria.  These  processes  are  termed  denitrificatioTi. 
There  are  still  other  processes  by  which  the  nitrogen  is  not 
lost  from  combination,  but  is  changed  into  forms  in  which 'it 
is  not  available  to  the  plant.  In  the  absence  of  air  and  in 
the  presence  of  organic  matter,  many  bacteria  can  use  the 
oxygen  contained  in  nitrates  for  their  respiratory  processes, 
as  the  ordinary  anaerobic  bacteria  use  the  oxygen  of  sugar. 
This  ability  to  reduce  nitrates  to  nitrites  and  to  am- 
monia is  a  very  common  property  of  bacteria,  and  is  made 
use  of  in  the  detailed  study  of  organisms.  When  aerobic 
conditions  are  restored  in  the  soil,  the  ammonia  and  ni- 
trites will  be  reoxidized  by  the  nitrifying  bacteria.  There 
is  no  loss  of  nitrogen  in  the  process,  except  such  as  may 
occur  in  a  secondary  reaction  that  may  take  place  between 
the  nitrites  and  ammonia  in  which  the  nitrogen  of  both  com- 
pounds is  set  free.  It  is  not  certain  that  this  secondary 
reaction  is  of  any  importance  in  the  soil,  although  it  may  be 
elsewhere,  as  in  certain  methods  of  sewage  disposal. 

A  much  smaller  number  of  bacteria  are  able  to  reduce 
nitrates  to  free  nitrogen.  The  conditions  necessary  for 
the  process  are  first  the  presence  of  nitrate,  second  a  sup- 
ply of  organic  matter,  and  third  an  absence  of  free  oxygen. 
The  organic  matter  is  essential  to  furnish  the  energy  needed 
to  decompose  the  nitrate.  It  was  seen  that  the  nitrifying 
bacteria  obtain  energy  from  the  oxidation  of  ammonia  to 
nitrites  and  nitrates.  If  energy  is  set  free  in  a  chemical 
reaction,  energy  will  need  to  be  absorbed  to  carry  on  the 
reverse  operation.  In  the  presence  of  air  these  organisms 
use  the  free  oxygen  and  leave  the  nitrate  untouched. 

The  denitrifying  bacteria  are  found  in  the  soil  and  in 
manures,  especially  in  horse  manure.  It  is  not  believed 
that  the  process  is  of  great  economic  importance,  since  con- 


106  AGRICULTURAL  BACTERIOLOGY 

ditions  in  the  soil  essential  for  the  process  do  not  obtain 
for  any  length  of  time.  If  nitrates  were  added  to  a  rich 
soil  or  were  applied  simultaneously  with  barnyard  manure, 
a  portion  of  the  nitrogen  might  be  lost;  but  in  ordinary 
soils  no  great  loss  of  nitrogen  can  occur  because  of  this 
process. 

Many  soil  bacteria  can  obtain  the  nitrogen  needed  to 
build  their  cells  from  nitrates.  If  any  considerable  amount 
of  growth  of  the  organisms  takes  place  at  the  same  time 
the  demand  of  the  crop  for  nitrate  is  greatest,  the  crop  may 
be  limited  in  its  growth,  since  nitrogen  is  most  frequently 
the  limiting  element.  There  would  be  the  same  objection 
to  these  bacteria  as  to  weeds  among  a  cultivated  crop, 
namely,  the  removal  of  food  that  might  otherwise  be  used 
by  the  crop.  These  bacteria  ultimately  die  and  the  nitro- 
gen is  ammonified,  so  they  do  not  permanently  remove  the 
nitrogen  from  the  soil,  but  merely  take  it  temporarily  from 
the  reach  of  the  plant. 


CHAPTER  XI 
BARNYARD   MANURES   AND   SEWAGE   DISPOSAL 

Manures. — One  of  the  most  important  by-products  of  the 
farm,  as  far  as  fertility  of  the  soil  is  concerned,  is  the  ex- 
crement of  farm  animals  and  the  litter  that  is  used  as  an 
absorbent  in  the  stalls.  Manure  contains  the  four  elements 
necessary  for  the  maintenance  of  fertility  of  the  soil — ni- 
trogen, phosphorus,  potassium,  and  sulphur.  None  of  these 
is  available  for  the  plant  in  the  form  in  which  it  is  excreted 
by  the  animal,  but  must  undergo  decomposition  by  micro- 
organisms. Fresh  manure  is  harmful  to  plants  rather 
than  helpful.  The  elements  must  pass  through  the  cycle 
of  changes  that  have  been  previously  detailed. 

The  farmer  desires  to  conserve  the  value  of  the  manure  as 
far  as  possible,  and  should  handle  it  in  such  a  manner  that 
he  may  .return  to  the  soil  the  maximum  amount  of  the  fer- 
tilizing elements.  Loss  of  the  elements  may  occur  by  leach- 
ing of  the  piles.  This  is  true  for  all  the  elements.  Nitro- 
gen may  be  lost  by  being  converted  into  volatile  substances. 
The  farmer  should  also  remember  that  organic  matter  is 
of  value  to  the  soil  as  a  source  of  humus  and  to  furnish 
energy  for  classes  of  bacteria  yet  to  be  described. 

From  the  standpoint  of  the  kinds  of  microorganisms  that 
grow  in  manures,  this  animal  refuse  may  be  divided  into 
two  classes,  the  basis  of  division  being  the  amount  of  water 
it  contains.  Horse  and  sheep  manure  contain  a  smaller 
amount  of  water  than  cow  and  hog  manures.  Xhey  are 
also  more  porous  and  lose  water  more  rapidly.  .  The  solid 
excrement  of  the  cow  dries  slowly.     The  lack  of  moisture 

107 


108  AGRICULTURAL  BACTERIOLOGY 

and  the  porosity  of  manures  from  the  horse  and  sheep 
permit  the  introduction  of  air,  and  lience  favor  the  growth 
of  aerobic  organisms,  especialh^  molds.  The  respiration  of 
the  aerobic  forms  results  in  the  production  of  heat,  which 
is  not  readily  radiated  on  account  of  the  non-conductivity 
of  the  organic  matter.  As  the  temperature  increases  the 
more  rapid  growth  of  the  organisms  is  made  possible.  This 
growth  continues  until  the  decomposition  of  the  manure  is 
complete  and  the  loss  of  nitrogen  and  organic  matter  is 
marked.  These  so-called  hot  manures  are  subject  to  fire- 
fanging.  The  loss  of  organic  matter  can  be  prevented  by 
the  close  packing  of  the  piles  to  exclude  air,  or  by  the  ad- 
dition of  water.  In  the  absence  of  the  air  the  decomposition 
will  be  due  to  anaerobic  forms,  and  while  the  rotting  will  be 
complete  in  that  the  vegetable  matter  loses  its  identity, 
there  is  not  so  great  a  loss  as  under  aerobic  conditions. 

Cow  and  hog  manure  are  cold  manures  on  account  of 
their  high  moisture  content  and  their  close  texture,  giving 
no  opportunity  for  air  to  penetrate.  These  manures  do 
not  overheat  or  fire-fang.  In  two  piles  of  manure  of  the 
same  composition,  one  of  which  was  piled  loosely  while  the 
other  was  closely  packed,  the  following  losses  were  noted. 
The  loss  of  nitrogen  from  the  loose  pile  amounted  to  34 
per  cent,  and  the  loss  of  organic  matter  to  53  per  cent., 
while  from  the  closely  packed  pile  the  loss  of  nitrogen  was 
28  per  cent,  and  of  organic  matter  the  same. 

The  conservation  of  the  fertilizing  value  of  manures  in- 
volves the  stopping  of  the  processes  of  decomposition  short 
of  completion.  The  last  steps  in  decomposition  are,  as  has 
been  mentioned,  always  due  to  aerobic  organisms.  The  an- 
aerobic organisms  will  disintegrate  the  fibrous  materials  of 
the  manure  and  enable  it  to  be  easily  distributed  over  the 
soil.  In  the  anaerobic  processes  a  considerable  portion  of 
nitrogen,  phosphorus,  potassium,  and  sulphur  in  the  ma- 


SEWAGE  DISPOSAL  109 

nure  is  converted  into  soluble  products.  The  decompos- 
ing manure  should,  therefore,  be  protected  from  leaching. 
Thoroughly  packed  piles  that  expose  the  minimum  of  sur- 
face tend  to  conserve  the  value  of  the  manure.  The  ac- 
cumulation of  manure  in  deep  stalls  in  which  suflBcient 
litter  is  used  to  absorb  the  liquid  manure,  and  in  which 
the  constant  tramping  of  the  animals  excludes  the  air,  is 
undoubtedly  the  best  way  of  handling  manure.  It  can 
best  be  used  with  sheep  and  feeding  cattle  rather  than  with 
dairy  cows.  The  direct  application  of  the  fresh  manure  to 
the  land  is  also  an  excellent  method  of  conserving  its  fer- 
tilizing value. 

Sewage  disposal. — The  disposal  of  the  waste  material  of 
man  represents  an  important  problem  to  the  family  liv- 
ing in  the  country.  When  great  numbers  of  people  are 
crowded  together,  as  in  cities,  and  when  to  the  household 
waste  is  added  the  waste  of  great  industrial  establishments 
like  the  packing-houses  of  Chicago,  the  problem  becomes 
still  more  important.  The  organic  matter  in  this  material, 
ordinarily  called  sewage,  must  be  decomposed  by  the  action 
of  microorganisms  into  the  simple  mineral  substances,  the 
salts  of  nitric,  phosphoric,  and  sulphuric  acids.  The  de- 
composition of  the  organic  matter  must  be  so  controlled  that 
it  shall  not  become  a  nuisance  or  injurious  to  health. 

It  is,  of  course,  desirable,  from  the  standpoint  of  conser- 
vation of  the  elements  having  great  fertilizing  value,  that 
the  organic  matter  be  returned  to  the  soil.  In  many  of 
the  larger  Oriental  cities,  the  night  soil  is  collected  and 
carried  to  the  cultivated  lands  near  the  city.  This  process, 
commendable  as  it  may  be  from  the  standpoint  of  the  con- 
servation of  plant  food,  can  be  used  only  where  human 
labor  is  cheap. 

The  American  and  European  cities  use  water  as  a  vehicle 
to  transport  the   sewage   from   the   point   of   production 


110  AGRICULTURAL  BACTERIOLOGY 

through  the  sewers  to  the  place  of  disposal.  A  considerable 
amount  of  decomposition  occurs  in  the  sewers  as  the  sewage 
flows  through  them.  The  larger  amount  of  decomposition 
must,  however,  occur  in  the  soil,  in  water-courses  or  in  ar- 
tificial disposal  pjants.  In  all,  the  same  organisms  function. 
The  sewage  may  be  flooded  over  the  land  in  a  manner  com- 
parable to  the  application  of  water  in  irrigation.  The 
water  leaches  through  the  soil,  leaving  the  organic  matter 
behind,  there  to  be  decomposed  by  the  soil  organisms. 
Sandy  land  is  desirable  for  the  successful  use  of  this 
method  of  sewage  disposal.  From  the  open  soil  the  water 
passes  quickly,  while  the  air  drawn  into  the  pore  spaces 
facilitates  the  decomposition  process.  Within  a  short  time 
this  change  is  effected.  If  a  fresh  application  of  sewage 
is  then  made,  the  soluble  products  resulting  from  the  first 
will  be  removed,  and  another  quantity  of  organic  matter 
will  be  left  in  the  soil. 

The  process  can  be  continued  indefinitely;  for,  owing  to 
the  highly  aerobic  condition  of  the  sand,  decomposition  is 
complete.  If  an  attempt  is  made  to  employ  a  close-grained 
soil  for  such  purposes,  failure  will  result.  The  organic  mat- 
ter left  by  the  percolating  sewage  will  not  be  completely  de- 
composed, because  of  the  small  supply  of  oxygen,  and  the 
residue  will  increase  in  amount.  Soon  the  land  will  be- 
come of  no  value  for  the  disposal  of  sewage.  The  cities  of 
Berlin  and  Paris  dispose  of  a  portion  of  their  sewage  by 
applying  it  to  sandy  land.  The  farm  home  can  use  this 
same  method  with  success  if  it  is  provided  with  a  modern 
water  supply,  so  that  water  can  be  employed  to  carry  the 
sewage  on  to  the  land. 

In  most  cities  the  sewage  is  turned  into  a  body  of  water, 
and  the  decomposition  processes  occur  in  the  liquid  rather 
than  in  the  soil.  If  the  body  of  water  is  large  in  proportion 
to  the  volume  of  sewage,  the  decomposition  will  take  place 


SEWAGE  DISPOSAL  111 

without  the  production  of  ol)jeetionable  odors  or  without 
injury  to  the  water  life.  If  the  amount  of  sewage  is  large 
in  proportion  to  the  water,  the  organisms  will  soon  exhaust 
tlie  oxygen,  and  the  decomposition  will  not  be  complete. 
Products  having  offensive  odors  and  an  injurious  action  on 
the  higher  animal  forms  of  the  water  will  be  produced. 

The  application  of  sewage  to  the  land  increases  its  fer- 
tility. On  the  sewage  farms  great  crops  of  grasses  and 
roots  may  be  raised.  The  addition  of  sewage  to  a  stream 
will,  of  course,  produce  an  increase  in  the  number  of  bac- 
teria. This  will  cause  an  increase  in  the  forms  that  live 
on  bacteria,  such  as  the  protozoa.  The  greater  number  of 
these  low  animal  forms  will  cause  an  increase  in  the  Crus- 
tacea that  serve  as  food  for  fish.  Hence  the  addition  of 
not  too  large  quantities  of  sewage  to  a  body  of  water  us- 
ually results  in  an  increase  in  the  number  of  fish.  If  these 
are  consumed  as  food,  some  portion  of  the  organic  matter  is 
again  made  use  of  by  man,  and  is  not  wholly  lost.  The  farm 
home  can  make  use  of  this  method  for  the  disposal  of  its 
sewage  if  a  body  of  water  of  some  size  is  available.  In 
case  any  city  draws  its  water  supply  from  this  source,  it 
should  not  be  used  for  the  disposal  of  household  sewage, 
because  of  the  danger  of  spreading  typhoid  fever,  as  will  be 
explained  later. 

If  the  sewage  is  allowed  to  undergo  partial  or  complete 
decomposition  before  it  is  discharged  into  a  body  of  water, 
a  much  greater  amount  of  sewage  can  be  added  to  the  water 
without  injuring  it  in  any  way.  Since  it  is  not  easy  to 
establish  conditions  so  that  the  decomposition  can  be  car- 
ried out  by  aerobic  organisms,  as  in  the  soil,  the  larger  part 
of  the  decomposition  is  allowed  to  take  place  under  anaer- 
obic conditions  in  large  tanks,  called  septic  tanks  because 
the  processes  are  carried  on  by  bacteria.  The  tanks  are  so 
arranged  that  the  sewage  flows  slowly  through  them;  the 


112 


AGRICULTURAL  BACTERIOLOGY 


solid  matter  settles  on  the  bottom  and  forms  a  sludge. 
There  soon  accumulates  on  the  surface  a  scum  in  which  a 
portion  of  the  gases  formed  in  the  decomposition  is  held. 
This  excludes  the  air  in  a  very  perfect  manner.     If  the 


A  Septic  Tank 


The  larger  compartment  is  the  septic  tank  proper  in  which  the  organic  matter 

of    the    sewage    is    exposed    to    bacterial    action.     The    second    compartment    or 

dosing  chamber  is  gradually  filled  from  the  septic  tank  and  then  emptied  by  the 

automatic  syphon  into  tile  drains 

sewage  is  allowed  to  remain  in  the  tank  from  twenty-four 
to  forty-eight  hours,  the  solid  matter  will  be  liciuefied,  the 
protein  changed  to  ammonia,  the  carbohydrates  to  acids 
and  gases.  The  tanks  are  frequently  called  digestion  tanks 
because  of  the  nature  of  the  changes  that  go  on  in  them. 
The  effluent  from  the  tank  is  turbid  and  has  a  disagreeable 
odor.  This  partially  decomposed  material  is  often  turned 
into  a  body  of  water,  or  it  may  be  so  treated  that  the  de- 
composition will  be  more  complete.  The  more  complete 
changes,   which   include  such   processes   as   the   oxidation 


SEWAGE  DISPOSAL  113 

of  ammonia  to  nitrates,  can  go  on  only  in  the  presence  of 
air.  The  sewage  may  be  conducted  on  to  filter  beds  of 
porous  material  such  as  cinders,  through  which  it  is  al- 
lowed to  trickle  slowly.  The  final  stages  of  decomposition 
here  take  place,  and  the  effluent  from  the  filter  beds  is  as 
clear  as  water  and  is  harmless  when  added  to  water  in  any 
amount,  as  far  as  the  water  life  is  concerned. 

The  decomposition  may  be  carried  on  entirely  under 
aerobic  conditions.  This  is  accomplished  by  conducting 
the  sewage  into  tanks  having  false  bottoms  of  a  porous  ma- 
terial through  which  air  can  be  forced.  Under  such  con- 
ditions there  soon  becomes  established  a  bacterial  flora  that 
is  capable  of  immediately  decomposing  the  organic  matter. 
After  a  period  of  aeration,  the  air  is  turned  off.  The  bac- 
teria settle  rapidly,  so  that  the  upper  two  thirds  of  the  con- 
tents of  the  tank  can  be  drained  off,  carr^'ing  the  soluble 
•products,  and  leaving  the  bacteria,  to  act  quickly  and  com- 
pletely on  the  next  quantity  of  organic  matter  presented 
to  them.  This  process  is  called  the  * '  activated  sludge ' '  pro- 
cess. 

The  farm  home  will  find  it  most  convenient  to  use  the 
septic  tank  for  the  disposal  of  the  sewage,  and  to  apply  the 
effluent  of  the  tank  either  to  the  surface  of  the  soil  or  be- 
neath the  surface  by  means  of  tile.  It  is  necessary  to 
establish  conditions  that  will  be  favorable  to  the  growth  of 
the  essential  classes  of  bacteria.  The  installation  of  such  a 
plant  is  a  separate  problem  for  each  home.  All  that  can 
here  be  done  is  to  point  out  the  necessary  conditions  that 
must  be  established.  The  tank  must  be  of  such  a  size  that 
it  will  hold  at  least  twice  the  amount  of  sewage  produced 
daily.  Before  the  sewage  passes  into  the  septic  tank,  it  is 
desirable  to  have  it  flow  through  a  grease  trap  to  remove 
the  fat  that  is  found  in  the  kitchen  waste ;  for  the  grease  is 
quite  resistant  to  decomposition  and  may  clog  the  drain  tile. 


114  AGRICULTURAL  BACTERIOLOGY 

The  tank  must  be  so  arranged  that  the  sewage  will  enter 
without  disturbing  the  sediment  or  the  layer  of  scum.  The 
inlet  must  be  below  the  surface,  and  cross-partitions  should 
be  placed  in  the  tank  to  prevent  currents  and  to  keep  all 
portions  of  the  sewage  in  the  tank  for  the  same  time.  A 
second  chamber  is  provided,  into  which  sewage  enters  from 
the  first  tank.  The  septic  tank  proper  is  thus  kept  con- 
tinually full. 

If  the  digested  sewage  is  applied  to  the  surface  of  the 
soil  or  discharged  into  underdrains,  it  is  necessary  to  dis- 
charge it  at  intervals  rather  than  constantly,  so  as  to  give 
the  water  time  to  drain  aw^y  and  the  air  to  enter  in  order 
that  the  decomposition  may  be  completed.  The  second  tank 
should  hold  from  one  third  to  one  quarter  of  the  daily 
volume  of  sewage.  It  is  called  the  dosing  chamber,  and 
some  means  must  be  provided  by  which  it  can  be  emptied 
when  full.  This  can  be  accomplished  by  installing  a  gate- 
valve  at  the  bottom  which  can  be  opened  and  closed  from 
the  surface.  A  more  convenient  arrangement  is  the  auto- 
matic syphon,  by  which  the  tank  is  emptied  whenever  the 
sewage  reaches  a  certain  depth. 

The  drains  into  which  the  sewage  is  discharged  are  placed 
from  eight  to  ten  inches  below  the  surface,  and  are  laid 
to  grade  with  open  joints,  as  in  the  case  of  ordinary  tile 
drains.  When  the  tank  is  emptied,  the  sewage  flows  into 
the  tile  and  fills  the  entire  length  of  the  drain.  It  passes 
out  of  the  open  joints  and  percolates  into  the  soil,  where 
the  last  steps  in  the  decomposition  of  the  organic  matter 
take  place,  just  as  in  the  filter  beds  used  in  the  disposal 
of  municipal  sewage.  If  the  sewage  were  allowed  to  flow 
constantly  from  the  tank  in  a  small  stream,  it  would  find  its 
way  into  the  soil  through  the  first  few  joints  of  the  tile; 
the  soil  in  the  immediate  neighborhood  would  be  kept  water- 
logged, and  the  oxidation  processes  could  not  go  on.     The 


SEWAGE  DISPOSAL  115 

soil  would  soon  become  clogged  with  the  undecomposed  or- 
ganic matter.  The  tiles  should  be  laid  near  the  surface  of 
the  soil,  so  that  oxygen  shall  be  available  for  the  aerobic 
bacteria. 

The  tile  may  be  laid  in  cinders  or  gravel  if  the  soil  is 
heavy  in  character.    A  sandy  soil  is  best  adapted  for  such 


Fig.  23.     The  Tile  Drain  of  a  Sewage  Purification  System 

The  tile  are  laid  near   the  surface  of  the  ground  and  surrounded  with  coarse 

material  like  gravel  or  cinders  in   order  that  the  sewage  may  pass  freely  out 

of   the   drains   into   the   ground    in    which   the    final   steps   in    its    decomposition 

take    place.     These    processes   require    an    abundance   of   oxygen 

a  disposal  system,  but  the  method  can  be  used  in  most 
types  of  soil.  Since  but  little  solid  matter  other  than  or- 
ganic enters  the  septic  tank,  the  accumulation  of  sludge  is 
slow,  and  the  tank  will  not  have  to  be  cleaned  for  several 
years.  The  drains  may  have  to  be  dug  up  and  the  tiles 
cleaned  once  in  three  or  four  years,  as  earthworms  bring  in 
a  good  deal  of  soil.  The  system  will  work  with  little  atten- 
tion, and  furnishes  a  means  by  which  the  farm  home  can 
dispose  of  the  household  sewage  in  a  convenient  and  harm- 


116  AGRICULTURAL  BACTERIOLOGY 

less  manner.  This,  together  with  an  abundant  and  well  ar- 
ranged water  supply,  adds  much  to  the  comfort  and  health- 
fulness  of  the  farm  home.  It  is  thus  possible  for  the  coun- 
try dweller  to  have  all  the  conveniences  that  the  city  home 
possesses  in  this  respect,  and  at  practically  no  greater  cost. 


CHAPTER  XII 
THE  FIXATION  OF  NITROGEN 

As  has  been  seen,  the  supply  of  nitrogen  in  the  soil  is  the 
result  of  processes  that  have  been  going  on  from  time  im- 
memorial under  natural  conditions.  When  human  activi- 
ties enter  into  consideration,  the  equilibrium  of  natural 
forces  is  upset.  The  decomposition  of  the  organic  matter 
goes  on  more  rapidly  and  more  completely  in  cultivated 
soil  than  in  the  virgin  forest  or  prairie.  The  more  aerobic 
conditions  favor  the  more  rapid  decomposition  of  the  humus 
that  has  accumulated,  and,  unless  care  is  taken  to  add  in- 
creased quantities  of  organic  matter  to  the  soil,  it  soon 
becomes  so  depleted  that  profitable  crops  can  no  longer  be 
grown. 

The  depletion  of  organic  matter  is  of  especial  importance 
from  the  standpoint  of  the  nitrogen  supply,  because  the 
humus  is  the  chief  source  of  nitrogen  for  the  soil  organisms. 
Some  nitrogen  is  lost  in  the  drainage  water,  and  also  in  the 
crop  removed  from  the  land.  It  is  probable  that  some  is 
also  lost  in  the  decomposition  of  nitrogenous  matter,  and 
certainly  in  the  process  of  denitrification.  The  depletion  of 
the  nitrogen  content  of  the  soil  has  been  considered  by  some 
observers  to  be  a  most  serious  problem.  Some  have  main- 
tained that  the  population  of  the  world  will  be  limited  be- 
cause of  the  constant  loss  of  nitrogen  from  the  soil.  It  is 
probable  that  such  fears  are  unfounded,  for  many  factors 
are  at  work  tending  to  maintain  the  nitrogen  content  of 
the  soil. 

117 


118  AGRICULTURAL  BACTERIOLOGY 

Chemical  processes  have  been  devised  by  which  the  nitro- 
gen and  the  oxygen  of  the  air  can  be  brought  into  combi- 
nation. The  most  successful  of  these  is  the  fixation  of 
.  nitrogen  by  electric  discharges.  Where  cheap  electric 
power  can  be  had,  nitrates  can  be  made  at  prices  that  en- 
able them  to  compete  with  the  natural  product  from  Chile. 
Large  quantities  of  such  nitrates  are  made  in  the  Scandi- 
navian countries,  where  water  power  is  abundant  and  con- 
ditions are  not  such  as  to  enable  the  power  to  be  used  for 
other  purposes.  Constant  progress  is  being  made  in  the 
development  of  methods  by  which  the  nitrogen  of  the  air 
is  made  to  combine  with  other  elements,  and  it  is  highly 
probable  that  the  world  has  little  to  fear  from  an  insufficient 
supply  of  combined  nitrogen  in  the  years  to  come. 

Nitrogen  added  to  the  soil  by  rains. — Every  electric  dis- 
charge occurring  in  the  atmosphere  results  in  the  produc- 
tion of  oxides  of  nitrogen.  These  and  the  ammonia  in  the 
air  are  returned  to  the  soil  in  the  rain  water.  It  has  been 
determined  that  from  three  to  six  pounds  of  nitrogen  are 
thus  added  to  each  acre  in  a  year.  About  70  per  cent,  of 
this  is  in  the  form  of  ammonia,  the  remainder  in  the  form 
of  oxides  of  nitrogen. 

Nitrogen  fixation  in  soil. — The  same  crop  can  be  grown 
on  the  land  for  hundreds  of  years;  the  y\eld  will  soon  reach 
a  level  below  which  it  will  not  fall.  This  level  is  usually 
established  by  the  rate  at  which  some  one  element  is  made 
available.  The  limiting  factor  most  frequently  is  nitro- 
gen. The  yield  of  the  crop  is  usually  larger  than  could  be 
accounted  for  by  the  amount  of  nitrogen  added  to  the  soil 
in  the  rain  water.  It  would  thus  seem  that  there  must  be 
factors  at  work  in  the  soil  that  tend  to  maintain  the  nitro- 
gen content.  In  the  latter  part  of  the  last  century,  Berthe- 
lot,  a  French  chemist,  studied  the  increase  of  nitrogen  in 
soils  on  which  no  crop  was  growing,  and  which  were  pro- 


FIXATION  OF  NITROGEN  119 

tected  from  the  rain.  He  found  that  a  constant  increase  in 
nitrogen  took  place.  He  estimated  that  the  nitrogen  thus 
added  to  the  soil  in  the  fields  amounted  to  from  50  to  75 
pounds  an  acre  each  year.  AVhen  the  soil  was  heated  no 
increase  in  nitrogen  occurred.  This  indicated  a  biological 
process. 

It  is  now  known  that  there  are  at  least  two  groups  of 
bacteria  in  the  soil  that  are  able  to  fix  nitrogen.  One  of 
these  is  an  anaerobic  group.  The  first  organism  studied 
was  given  the  name  of  Clostridium  Pasteurianus.  The  or- 
ganism will  grow  in  a  nutrient  solution  containing  inor- 
ganic salts,  which  supply  the  essential  mineral  elements,  and 
sugar,  which  supplies  the  energy.  No  nitrogen  need  be 
present  in  the  solution.  In  the  process  of  growth,  nitroge- 
nous organic  matter  is  formed,  and  since  the  only  source  of 
nitrogen  is  the  free  nitrogen  of  the  air,  the  organism  must 
in  some  way  bring  it  into  combination.  It  was  found  that 
for  every  gram  of  sugar  fermented  about  two  milligrams  of 
nitrogen  were  combined. 

Another  group  of  nitrogen-fixing  bacteria  in  the  soil  be- 
longing to  the  aerobic  type  is  known  as  the  Azotohactcr 
group.  Most  of  its  members  have  the  ability  to  form  a 
black  pigment ;  the  name  Azotohacter  chroococciim  has  been 
given  to  this  type.  This  type  is  more  efficient  in  fixing 
nitrogen  than  the  previous  group,  in  that  for  every  gram 
of  sugar  fermented  from  10  to  20  milligrams  of  nitrogen 
are  fixed.  Members  of  this  group  are  found  in  nearly  all 
soils;  they  are  more  abundant  in  the  more  fertile  soils. 
They  are  also  found  in  water,  frequently  in  combination 
with  green  algop.  It  is  supposed  that  they  live  in  a  symbi- 
otic relationship,  the  algae  furnishing  the  carbohydrate  to 
the  bacteria,  and  the  latter  nitrogen  in  an  available  form  to 
the  cells  of  the  algae.  Not-  only  can  sugar  be  used  as  a 
source  of  energy,  but  also  organic  acids.     It  is  thought  that 


120  AGRICULTURAL  BACTERIOLOGY 

cellulose  is  also  made  available  to  the  nitrogen-fixing  bac- 
teria by  the  cellulose-fermenting  bacteria  through  the  for- 
mation of  sugars. 

It  has  been  maintained  that  the  nitrogen-fixing  power  of 
a  soil  could  be  increased  by  inoculation  with  cultures  of 
these  organisms.  Such  a  hope  has  not  yet  been  realized. 
Their  action  in  the  soil  must  be  favored  by  the  establish- 
ment of  a  suitable  environment.  A  sufficient  supply  of 
both  phosphorus  and  potassium  is  essential,  as  is  organic 
matter  from  the  fermentation  of  which  they  may  obtain  the 
energy  necessary  for  the  combination  of  the  nitrogen.  As 
noted  in  the  discussion  on  manures,  it  is  desirable  to  add 
to  the  soil  as  much  organic  matter  as  possible,  irrespective 
of  whether  it  contains  any  of  the  four  elements  that  are 
known  to  be  most  important  from  the  standpoint  of  the  soil. 
One  important  role  of  the  organic  matter  is  to  favor  the 
growth  of  these  nitrogen-fixing  organisms.  There  is  good 
reason  to  believe  that  these  two  groups  of  bacteria  are  im- 
portant factors  in  the  maintenance  of  the  nitrogen  content 
of  the  soil,  rather  than  simply  scientific  curiosities,  as  some 
have  considered  them.  The  nitrogen  fixed  by  these  groups 
of  bacteria  is  built  into  organic  matter,  which  must  be 
ammonified  and  nitrified  before  the  nitrogen  drawn  from 
the  air  can  be  used  by  the  green  plant. 

Leguminous  plants. — It  has  long  been  recognized  that 
the  leguminous  plants  have  different  properties  from  the 
grains  and  grasses  in  that  they  are  able  to  produce  luxuri- 
ant crops  on  lands  on  which  the  non-legumes  will  make  but 
a  meager  growth.  They  also  seem  to  enrich  the  soil,  since 
the  yield  of  the  crop  following  them  is  often  greater  than 
that  obtained  from  the  same  land  on  which  a  non-legume 
had  been  grown.  This  property  has  led  to  the  inclusion  of 
some  type  of  leguminous  plant  in  most  systems  of  crop 
rotation.     It  was  found  by  Liebig,  the  father  of  agricultural 


FIXATION  OF  NITROGEN 


121 


Fig.  24.     Nodules  on  Soy  Beans 
The   nodules   are  large   and  rough  on  the  surface 


122  AGRICULTURAL  BACTERIOLOGY 

chemistry,  that  in  some  unknown  manner  the  leguminous 
plants  were  able  to  increase  the  content  of  the  soil  in  nitro- 
gen, and  that  they  seemed  to  have  sources  of  nitrogen  that 
were  not  open  to  other  classes  of  plants. 

It  had  also  long  been  known  that  there  were  commonly 
on  the  roots  of  the  leguminous  plants,  nodules  or  tubercles, 
which  were  usually  looked  upon  as  galls  similar  to  those 
produced  on  many  plants  by  the  stings  of  insects,  and  by 
other  causes  that  stimulate  the  growth  of  the  plant  cells  in 
the  immediate  vicinity  to  which  the  stimulus  is  applied. 
The  tubercles  were  thought  to  be  injurious,  or  at  least  not 
of  service  to  the  plant.  It  had  been  found  that  the  tu- 
bercles contained  bacteria.  Hellriegel  and  Wilfarth,  Ger- 
man investigators,  founds  in  their  study  of  the  ability  of 
different  plants  to  grow  in  the  absence  of  some  one  element, 
that  the  non-leguminous  plants  were  able  to  make  but  a 
slight  growth  in  the  absence  of  combined  nitrogen.  Some 
growth  would  always  take  place  because  of  the  content  of 
nitrogen  in  the  seed,  but  when  this  was  exhausted,  the 
plant  would  die  of  nitrogen  starvation.  When  legumes 
were  studied,  the  results  in  some  instances  were  identical 
with  those  obtained  with  the  non-legumes,  while  at  other 
times  the  legumes  showed  an  ability  to  grow  in  the  absence 
of  combined  nitrogen  in  the  soil.  No  prediction  could  be 
made  as  to  the  outcome  of  any  experiment  when  legumes 
were  used,  as  could  be  done  with  the  other  kinds  of  plants. 

These  investigators  found  that  the  ability  of  the  legumi- 
nous plants  to  grow  in  the  absence  of  combined  nitrogen  was 
correlated  with  the  presence  of  tubercles  on  the  roots  of  the 
plant.  If  the  soil  was  sterilized,  no  tubercles  appeared, 
and  the  plant  was  unable  to  grow  except  when  nitrogenous 
fertilizers  had  been  added  to  the  nitrogen-free  soil.  A  few 
drops  of  the  leachings  from  the  soil  on  which  the  legume  in 
question  had  been  grown  was  sufficient  to  induce  tubercle 


FIXATION  OF  NITROGEN 


123 


P     ALFALM 
pUNlNOCULATCO 


ALFALFA 
INOCULATED 


Fig.   25.     Eflect  of   Inoculation   on   Alfalfa 

The  soil  contained  no  nitrogen.      By  the  aid  of  the  nodule- forming  bacteria  th< 

inoculated  plants  have  been  able  to  secure  nitrogen  from  the  air 


124  AGRICULTURAL  BACTERIOLOGY 

formation  and  consequently  growth.  If  the  leachings  were 
heated,  no  effect  was  noted.  It  was  thus  evident  that  the 
causal  factor  was  a  biological  one.  Soon  after  the  discovery 
of  the  relation  of  the  nodule  to  the  nitrogen  needs  of  the 
plant,  the  nodule-forming  bacteria  were  isolated  by  the 
Dutch  bacteriologist,  Beyjerinck. 

When  leguminous  plants  are  spoken  of,  the  cultivated 
legumes  come  to  mind,  such  as  the  clovers,  alfalfa,  the  peas 
and  beans,  the  vetches,  lupines,  and  serradella.  The  native 
flora  of  all  soils  and  of  all  parts  of  the  world  is  made  up 
in  large  part  of  leguminous  plants.  It  has  been  determined 
that  20  per  cent,  of  the  flora  of  the  Western  prairies  con- 
sists of  wild  or  native  legumes,  while  still  higher  figures 
have  been  obtained  in  the  Eastern  States.  In  size  they 
vary  from  the  smallest  clovers  to  full  sized  trees,  such  as 
the  honey  locust.  All,  as  far  as  is  known,  have  the  same 
relation  to  the  nodule-forming  bacteria,  and  possess  the 
ability  to  use  the  free  nitrogen  of  the  air.  Leguminous 
plants  are  found  growing  on  every  type  of  soil.  Some  are 
adapted  to  acid  soils,  while  others  grow  best  on  alkaline 
soils.  Many  are  adapted  to  high  land,  and  a  few  are 
water  plants. 

It  is  certain  that  the  leguminous  plants  and  the  associated 
bacteria  have  been  the  chief  factors  in  the  gradual  storing 
of  nitrogen  in  the  soil.  Under  their  influence,  the  elemen- 
tal nitrogen  of  the  air  is  brought  into  combination  in  the 
form  of  proteins,  which,  as  they  have  undergone  decompo- 
sition in  the  soil,  have  left  a  residue  of  humus. 

The  legumes  are  differentiated  from  the  grasses  and 
grains  by  their  peculiar  relation  to  a  group  of  bacteria  and 
by  their  composition.  Both  the  seed  and  vegetative  parts 
contain  much  more  nitrogen  than  is  the  case  with  the  non- 
leguminous  plants,  as  is  shown  in  the  following  table : 


FIXATION  OF  NITROGEN 


125 


Average  Fertilizhuj  Constituents  and  Digestible  Nutrients 
to  the  Ton 


Fertilizing  Constituents 

Digestible  Nutrients 

in  One  Ton 

in  One  Tou 

Kind  of  Forage 

Nitro- 
gen 

Phos- 
phoric 
acid 
PjCs 

Pot- 
ash 
KsO 

Crude 
pro- 
tein 

Carbo- 
hy- 
drates 

Fat 

Total 

lbs. 

lbs. 

lbs. 

lbs. 

lbs. 

lbs. 

lbs. 

Alfalfa  hay 

47.6 

10.8 

44.6 

212.0 

780.0 

18.0 

1,032.0 

Red    clover    hay. 

41.0 

7.8 

32.6 

152.0 

786.0 

36.0 

1,018.0 

Soybtan    hay 

51.2 

13.6 

46.6 

234.0 

784.0 

24.0 

1,072.0 

Field-peas    hay.  . 

48.4 

13.4 

24.8 

244.0 

802.0 

38.0 

1.132.0 

Corn    fodder     .  . 

21.4 

6.6 

17.8 

60.0 

946.0 

30.0 

1,074.0 

Timothy    hay    .  . 

19.8 

6.2 

27.2 

60.0 

856.0 

24.0 

990.0 

Kentucky    blue- 

grass    hay     .  . 

26.6 

10.8          42.0 

94.0 

870.0 

30.0 

1.032.0 

Oat   hay    

26.8 

16.0         65.4 

90.0 

762.0 

34.0 

928.0 

Inoculation  of  the  soil. — It  is,  of  course,  evident  that  if 
the  soil  does  not  contain  the  bacteria  that  form  the  nodules 
and  bring  the  free  nitrogen  of  the  air  to  the  service  of  the 
plant,  the  legume  must  draw  all  of  its  supply  from  the  soil. 
If  the  crop  is  removed,  the  soil  will  be  more  rapidly  de- 
pleted of  its  nitrogen  content  than  with  a  grain  crop,  and 
if  the  crop  is  turned  under,  no  increa.se  in  the  nitrogen 
content  of  the  soil  will  have  taken  place.  If  the  legumes 
are  to  be  used  to  enrich  the  soil,  the  fields  must  contain  the 
bacteria.  The  recognition  of  this  fact  led  to  the  inocula- 
tion of  the  soil.  At  first  soil  from  a  field  on  which  the 
legume  in  question  had  been  grown  was  employed.  Later 
the  use  of  pure  cultures  of  the  bacteria  was  attempted. 
For  many  years  it  met  with  little  success,  due,  apparently, 
to  the  fact  that  the  bacteria  on  artificial  cultivation  lost 
their  ability  to  form  the  nodules.  IVIore  recently  improved 
methods  of  growing  the  bacteria  in  the  laboratory  have  been 
devised,  and  at  present  the  use  of  artificial  cultures  for  the 
inoculation  of  legumes  is  successful. 

The  success  attained  in  the  use  of  the  cultures  for  the 
inoculation  of  seed  depends  on  many  factors,  chief  among 


126  AGRICULTURAL  BACTERIOLOGY 


Fisr.  2G.     Effect  of  Inoculation  on  Peas 

TVe  soil  of  the  field  was  a  light  sand,  very  low   in  nitrogen.     The  inoculation 
of  the  seed  resulted  in  a  luxuriant  crop.     Without  the  bacteria  the  crop  was 

a  failure 


FIXATION  OF  NITROGEN  127 

which  is  the  vitality  of  the  culture.  If  it  is  old  and  made 
up  of  weakened  bacteria,  good  results  will  not  be  obtained. 
The  culture  must  be  grown  under  favorable  conditions  and 
be  fresh  to  give  good  results.  It  is  possible  to  bring  large 
numbers  of  the  bacteria  into  intimate  contact  with  the  seed 
by  inoculating  it  directly  with  the  culture. 

The  bacteria  that  will  produce  the  nodules  on  the  roots 
of  one  legume  will  not  necessarily  do  so  on  a  different 
legume.  The  legumes  may  be  divided  into  separate  groups 
within  which  the  bacteria  from  one  legume  will  produce 
nodules  on  the  roots  of  the  other  legumes  in  the  group,  or 
*' cross-inoculate."  The  following  list  gathers  the  common 
leguminous  plants  into  groups  that  cross-inoculate : 

1.  To  inoculate  red  clover,  use  the  bacteria  from  red 
clover,  mammoth  red,  alsike,  crimson,  Egyptian,  or  white 
clover. 

2.  To  inoculate  alfalfa,  use  the  bacteria  from  alfalfa, 
white  sweet  clover,  yellow  sweet  clover,  bur  clover,  yellow 
trefoil,  or  fenugreek. 

3.  To  inoculate  garden  pea,  use  the  bacteria  from  garden 
pea,  field  pea,  hairy  vetch,  spring  vetch,  wild  vetch,  broad 
bean,  lentil,  sweet  pea,  or  perennial  pea. 

4.  To  inoculate  cowpea,  use  the  bacteria  from  cowpea, 
partridge-pea,  peanut,  Japanese  clover,  velvet  bean,  lima 
bean,  wild  indigo,  or  tick  trefoil. 

^  5.  To  inoculate  garden  bean,  use  the  bacteria  from  gar- 
|den,  field,  navy,  kidney,  or  scarlet  runner  bean. 

6.  To  inoculate  lupine,  use  the  bacteria  from  lupine,  ser- 
radella,  or  wild  lupine. 

7.  To  inoculate  soybean,  use  only  the  bacteria  from  the 
soybean. 

The  bacteria  enter  the  plant  through  the  root  hairs. 
They  stimulate  the  growth  of  the  cells  at  the  point  of  en- 
trance, and  the  nodule  is  produced.     If  this  nodule  is  ex- 


Fig.  27.     Effect  of  Inoculation  on  Sweet  Clover 

The  crop  was  grown  on  a  very  poor  sandy  soil.     Inoculation  enabled  the  plant 

to   draw   the   necessary   nitrogen   from  the  air 

19S 


,  FIXATION  OF  NITROGEN  129 

amined  under  the  microscope,  the  plant  cells  will  be  found 
filled  with  myriads  of  motile  bacteria,  which  in  the  young 
nodules  are  rod-shaped,  but  in  the  older  ones  assume  ab- 
normal shapes  known  as  hacteroids.  In  some  not  well  un- 
derstood manner,  the  bacteria  are  able  to  obtain  their  nitro- 
ofen  from  the  air  and  to  make  it  available  to  the  plant. 
The  bacteria  derive  from  the  plant  the  fermentable  mate- 
rial necessary  to  secure  the  energry  demanded  for  the  fix- 
ation of  the  nitrogen.  The  relation  is  thus  a  mutually  help- 
ful or  a  symbiotic  one. 

The  plant  can  thus  obtain  a  sufficient  supply  of  nitrogen 
to  make  a  good  growth,  but  when  growing  under  natural 
conditions  the  plant  derives  a  greater  or  less  amount  of  its 
nitrogen  from  the  soil  in  the  same  way  as  do  other  plants. 
No  one  can  state  the  proportion  of  nitrogen  taken  from  the 
air  or  from  the  soil  under  any  given  set  of  conditions.  All 
that  can  be  said  is  that  the  plant  is  unable  to  use  the  free 
nitrogen  of  the  air  unless  the  nodules  are  present  on  the 
roots.  If  the  nodules  are  few,  a  small  part  of  the  nitrogen 
may  come  from  the  air,  while  if  the  roots  are  well  covered 
with  nodules,  the  plant  will  undoubtedly  take  the  major 
part  of  its  nitrogen  from  the  air.  Every  farmer  should 
make  an  effort  to  have  all  the  legumes  he  may  grow  well 
inoculated. 

Other  conditions  must  be  made  as  favorable  for  the  le- 
gume as  possible.  There  should  be  an  adequate  supply  of 
potash  and  phosphorus  in  the  soil,  and  the  reaction  should 
be  favorable  for  the  particular  legume.  When  these  con- 
ditions are  met  and  the  appropriate  bacteria  are  present  or 
have  been  added,  nodule  development  should  be  abundant. 
It  must  be  remembered  that  the  only  way  in  which  the 
legume  can  increase  the  fertility  of  the  soil  is  with  reference 
to  the  single  element  nitrogen.  A  leguminous  crop  may  be 
grown  on  a  field  and  be  removed,  and  the  soil  remain  as 


130  AGRICULTURAL  BACTERIOLOGY 

high  in  nitrogen  as  before  the  crop  was  grown;  but  this 
can  never  be  true  of  potassium,  phosphorus,  and  sulphur. 

The  legume  bacteria  are  motile.  There  is,  however,  no 
reason  to  believe  that  they  can  pass  through  the  soil  in  a 
horizontal  direction  for  any  distance.  The  plant  root  must 
come  in  contact  with  the  bacteria  before  infection  can  take 
place.  Since  the  plant  roots  do  not  fill  all  the  spaces  of  the 
soil,  it  is  essential  that  the  soil  contain  great  numbers  of 
these  organisms  in  order  that  an  abundance  of  nodules  may 
be  formed.  If  artificial  inoculation  is  to  be  resorted  to,  it 
is  important  to  bring  the  organisms  in  intimate  contact  with 
the  roots  of  the  young  plant.  This  is  best  accomplished  by 
the  inoculation  of  the  seed  rather  than  by  the  inoculation 
of  the  soil.  In  the  case  of  inoculation  with  soil,  the  seed 
may  be  moistened  slightly  and  the  fine  soil  thoroughly 
mixed  with  it.  The  seed  should  be  treated  shortly  before 
it  is  to  be  sown.  The  pure  cultures  are  usually  added  to 
water,  which  is  sprinkled  over  the  seed.  It  must  be  re- 
membered that  unfavorable  conditions,  such  as  drying  and 
sunlight,  may  destroy  the  organisms  on  the  seed.  If  soil 
containing  the  organisms  is  available  in  unlimited  amounts, 
it  may  be  broadcasted  over  the  field,  or  it  may  be  applied 
with  a  drill  and  well  harrowed  in,  so  as  to  mix  it  as  inti- 
mately as  possible  with  the  soil. 

No  very  definite  direction  can  be  given  as  to  the  amount 
of  soil  that  should  be  used  in  the  inoculation,  since  this  will 
be  determined  by  the  number  of  bacteria  in  it.  In  case 
it  is  broadcasted  over  the  land,  several  hundred  pounds  an 
acre  should  be  added.  It  has  been  found  in  experimental 
work  in  the  greenhouse  that  the  bacterial  content  of  the 
soil  to  which  sugar  has  been  added  may  reach  a  point  where 
one  half  pound  an  acre  will  produce  a  good  inoculation. 

Another  practical  method  of  securing  optimum  conditions 
favorable  to  the  growth  of  a  different  kind  of  legume  is  to 


FIXATION  OF  NITROGEN 


131 


sow  a  small  quantity  of  the  seed  in  question  with  the  regu- 
lar crops.  Thus,  if  it  is  desired  to  secure  a  catch  of  alfalfa 
on  soil  that  has  not  grown  this  crop,  instead  of  inoculation 
with  a  pure  culture  or  infected  soil,  some  farmers  follow 


ORGANiq    MATTER 


ANIMAL5 


nit  CMtXM>  MTROCtn  ANJ 

0KIOC&  or  runuccN  t-tCAPt     | 

TOAiK  TRLt  NiTROGtN  nXATON 


jfZZfe^: 


CXCRtMCNT 
SOLID       UOWO    BODY 

PUTREfACTlON  AND  DECAY 

AMMONiriCATKDN      AMMONIA    igM, 


DCNITRIFICATlON 


NITRiriCATlON 


-NITP1TC5  N,0. 


rNlTRATES  N,0, 

'     I    *l     I     I     f — • — ■ — ■ — ' 


Fig.   28.     The  Cycle  of  Nitrogen 


After  Wright. 


the  practice  of  sowing  a  small  quantity  of  alfalfa  seed  with 
all  of  their  grain  crops,  even  if  the  land  is  seeded  down  to 
red  clover.  In  a  few  years  this  preliminary  inoculation  suf- 
fices to  infect  the  soil  sufficiently  so  that  inoculation  of  the 
crop  can  be  readily  secured  later. 

The  matter  of  inoculation  is  especially  important  when  a 
new  legume  is  to  be  grown  or  when  a  legume  is  to  be  sown 
on  a  field  on  which  it  has  not  been  grown  for  a  number  of 
years.  The  bacteria  are  able  to  grow  in  the  soil  itself. 
Experience  has  shown  that  they  gradually  decrease  in  num- 
ber, and  after  five  or  six  years  will  be  so  diminished  that 
inoculation  is  advisable  if  the  legume  is  to  be  grown  again. 

It  has  been  shown  that  the  composition  of  the  plant  is 
changed  b}'  the  presence  of  the  nodules  in  that  the  nitro- 


132  AGRICULTURAL  BACTERIOLOGY 

gen  content  of  the  aerial  parts  of  the  plants  bearing  nodules 
is  higher  than  plants  on  which  nodules  are  not  present. 
The  composition  of  non-legumes  growing  with  legumes  is 
also  changed  in  the  same  manner. 

A  few  non-leguminous  plants  may  bear  nodules  on  the 
roots,  and  apparently  have  the  same  relation  to  free  nitro- 
gen as  do  the  legumes.  The  most  important  of  these  are 
the  alders.  The  development  of  the  nodules  is  very  sparse, 
as  a  rule. 

The  legume  furnishes  the  cheapest  way  of  preventing  the 
rapid  reduction  of  the  nitrogen  content  of  the  soil.  Where 
sandy  lands  are  to  be  reclaimed  and  worn-out  soils  restored, 
the  legume  is  to  be  considered  a  most  important  factor. 
The  nitrogen  thus  added  to  the  soil  is  estimated  to  cost 
only  from  one  half  to  five  cents  a  pound,  as  opposed  to  the 
usual  commercial  price  which  is  from  25  to  30  cents. 


PART  III 

THE  RELATION  OF  MICROORGANISMS 
TO  FOODS 


CHAPTER  XIII 
THE  CONTAMINATION  OF  FOODS 

The  decomposition  of  organic  matter  is  due  to  the  action 
of  microorganisms  that  utilize  the  various  compounds  as 
food,  and  leave,  as  a  result  of  their  life  processes,  more  sim- 
ple substances,  or  hy -products.  Since  most  of  these  changes 
affect  the  quality  of  foods  that  are  used  by  man,  or  even  the 
domestic  animals,  it  is  desirable  to  protect  food  supplies  in 
general,  so  far  as  practicable,  from  the  action  of  such 
microorganisms.  Especially  in  the  temperate  zone  is  this 
question  of  food  preservation  of  great  importance,  for  the 
st'ason  during  which  plant  growth  takes  place  is  short,  and 
vegetable  matter  must  be  stored  for  use  during  the  colder 
period  of  the  year.  Under  the  complex  conditions  in  which 
we  now  live,  the  question  of  protection  of  food  during  the 
process  of  distribution  is  likewise  of  great  importance. 

While  the  action  of  most  microorganisms  in  food  sup- 
plies does  not  enhance  the  nutritive  properties  of  foods, 
certain  types  are  used  to  advantage  in  the  preparation  of 
some  foods,  as  in  the  fermentation  industries,  in  which  the 
raw  materials  are  transformed  by  the  action  of  living  or- 
ganisms. Some  by-products  are  used  as  food,  or  they  may 
be  of  service  in  the  preparation  of  food,  as  is  the  case  with 
carbon-dioxide,  formed  by  the  action  of  yeast  on  sugar, 
which  serves  as  a  leaven  to  ''raise"  or  lighten  the  dough  in 
bread-making. 

Milk. — In  the  following  pages  the  discussion  is  limited 
chiefly  to  milk  and  dairy  products,  as  virtually  all  phases 
of  the  relation  of  microorganisms  to  foods  are  well  illus- 

135 


136  AGRICULTURAL  BACTERIOLOGY 

trated  with  milk  and  its  products.  There  are  special  rea- 
sons why  a  detailed  discussion  of  the  action  of  microorgan- 
isms on  this  food  product  is  desirable.  Milk  is  one  of  the 
most  important  foods  in  the  dietary  of  the  American  and 
European  people.  It  forms  about  one  sixth  of  the  food 
of  the  population  of  this  country,  and  for  children  a  much 
greater  proportion  of  their  nutriment.  One  milch-cow  is 
kept  for  each  4.5  persons.  A  large  portion  of  the  milk 
consumed  is  used  as  raw  milk^  and  hence  its  contamination 
with  disease-producing  bacteria  is  of  great  importance. 
Again,  its  preservation  is  a  problem  that  is  presented  to 
the  producer  and  to  the  consumer  daily;  for,  in  the  pro- 
duction and  handling  of  milk,  it  becomes  seeded  with  great 
numbers  of  bacteria,  which  find  in  it  a  most  favorable  place 
for  growth.  The  manufacture  of  butter  and  cheese  was 
originally  carried  out  on  the  farm.  Their  preparation  has 
now  been  largely  removed  therefrom ;  but  the  farmer  is  still 
the  producer  of  the  raw  material,  the  quality  of  which  de- 
termines the  quality  of  the  product. 

Factors  governing  decomposition. — In  the  decomposition 
of  any  substance  the  rapidity  of  the  changes  involved  are 
determined  by  the  number  of  organisms  from  foreign 
sources  that  are  brought  in  contact  with  the  material,  and 
by  the  rapidity  with  which  growth  occurs,  since  decompo- 
sition processes  can  not  occur  without  growth,  no  matter 
how  great  the  initial  contamination  of  the  food.  The  ques- 
tion of  food  preservation,  therefore,  may  be  divided  into 
two  divisions :  first,  the  contamination  of  the  food ;  second, 
the  destruction  of  the  microorganisms  contained  in  the  food 
or  the  inhibition  of  their  growth. 

The  first  is  especially  important  with  liquid  foods,  such 
as  milk,  because  the  organisms  can  be  uniformly  incorpo- 
rated with  the  liquid,  and  their  growth  will  not  be  limited 
to  any  one  point,  as  in  the  case  of  solid  foods.     Again,  when 


CONTAMINATION  OF  FOODS  137 

once  introduced,  they  can  not  be  removed  therefrom  as 
from  the  surface  of  a  solid. 

The  source  of  contamination  of  foods  in  general  is  readily 
traced  to  contact  with  matter  from  the  soil,  water,  or  the 
contents  of  the  alimentary  tract  of  animal  life.  These  ma- 
terials harbor  the  bacterial  life  that  is  the  cause  of  the 
changes  involved,  and  if  foods  can  be  kept  from  direct  con- 
tact with  such  organic  wastes,  it  is  comparatively  easy  to 
prevent  in  large  measure  the  decomposition  changes  that 
will  otherwise  occur.  In  the  protection  and  care  of  food 
products,  it  is  desirable  to  do  only  those  things  that  are  of 
real  necessity  and  value,  rather  than  to  waste  time  and 
effort  in  carrying  out  a  mode  of  procedure  that  is  unneces- 
sarily refined.  So  much  exaggeration  is  fre<iuently  found 
in  the  public  prints,  relative  to  germ  life  and  its  dangers, 
that  not  infrequently  unnecessarj^  alarm  is  engendered  in 
the  minds  of  many  people.  This  makes  it  important  that 
consideration  be  given  to  the  various  sources  of  contamina- 
tion from  which  milk  becomes  seeded  with  bacteria.  It  is 
especially  essential  tliat  the  relative  importance  of  the  vari- 
ous sources  of  contamination  be  understood,  for  if  improve- 
ment of  the  product  is  to  be  attempted,  the  first  efforts 
should  be  directed  to  those  sources  from  which  the  greatest 
return  for  money  and  labor  expended  will  be  obtained. 

All  milk  will  contain  bacteria,  no  matter  how  carefully  it 
may  be  produced.  It  is  impossible  to  maintain  the  same 
standards  of  cleanliness  in  the  stable  as  in  the  kitchen,  the 
bakery,  and  the  meat-shop.  More  than  any  other  food, 
milk  is  subject  to  contamination  with  materials  rich  in  bac- 
teria. 

Contamination  of  milk  from  the  interior  of  the  udder. — 
When  milk  leaves  the  luilk-prodiicing  cells  of  the  udder  of 
a  healthy  animal,  it  is  probably  free  from  these  organisms; 
but  this  condition  does  not  long,  obtain,  for  before  it  is 


138 


AGRICULTURAL  BACTERIOLOGY 


drawn  from  the  animal  it  comes  in  contact  with  the  bacteria 
that  have  invaded  the  udder  through  the  opening  of  the 
teat    and    have    established    themselves    throughout    the 

spaces  or  channels  which  ramify 
through  this  organ.  The  greater 
number  of  organisms  are  found 
in  the  lower  portion  of  the  ud- 
der, in  the  milk  cistern  and  in 
the  large  milk  ducts.  The  open- 
ing of  the  teat  comes  in  contact 
witli  material  that  contains  the 
most  varied  kinds  of  bacteria, 
and  it  is  probable  that  the  milk 
duets  are  invaded  by  many 
kinds.  Only  certain  types,  how- 
ever, are  able  to  grow  in  the  ud- 
der, and  these  only  to  a  limited 
extent.  As  will  be  seen  later,  all 
body  fluids  have  a  germicidal  ac- 
tion. Tlie  germicidal  action  of 
milk  probably  explains  why  the 
growth  of  the  bacteria  that  in- 
vade the  udder  is  not  nearly  so 
rapid  as  one  would  expect  under 
the  favorable  conditions  with 
reference  to  food  and  tempera- 
ture. It  has  been  shown  that  no 
bacterial  increase  occurs  in  milk  for  a  period  after  it  is 
drawn.  This  has  usually  been  ascribed  to  the  germicidal 
action  of  the  milk.  Whatever  action  milk  may  exhibit  in 
this  direction,  it  is  of  small  importance  in  the  practical 
handling  of  the  product. 

The  kinds  of  bacteria  that  are  able  to  grow  in  the  udder 
are  not  those  that  are  actively  concerned  in  the  spoiling 


A  Section 
Udder 
The  milk  is  conducted  from  the 
secreting  cells  by  the  milk  ducts 
■which  empty  into  the  milk  cis- 
tern from  which  it  is  drawn 
through  the  teats.  Bacteria  en- 
ter the  teats  and  penetrate  into 
the  smallest  of  the  milk  ducts 


CONTAMINATION  OF  FOODS  139 

of  milk;  Iienco,  this  source  of  contamination  of  milk,  al- 
thoupfh  one  that  can  not  be  avoided,  is  of  small  commercial 
importance.  At  times  the  udder  may  be  invaded  by  bac- 
teria upon  which  the  milk  has  no  germicidal  action. 
Growth  will  then  be  unchecked  and  serious  trouble  may 
result. 

The  milk  at  the  time  of  withdrawal  generally  contains  a 
few  hundred  bacteria  per  cubic  centimeter.  Great  differ- 
ences in  individual  animals  are  to  be  noted.  In  the  same 
herd  two  animals  were  found  that  showed  an  average  bac- 
terial content  of  more  than  30,000  per  cubic  centimeter  dur- 
ing  a  period  of  over  one  year.  Another  animal,  kept  under 
the  same  conditions,  gave  milk  in  which  the  average  germ 
content  was  but  800  per  cubic  centimeter.  The  mixed  milk 
of  a  number  of  cows  will  contain  from  a  few  hundred  to  a 
thousand,  or  more  bacteria  per  cubic  centimeter,  even  when 
the  contamination  from  outside  sources  has  been  prevented 
as  far  as  is  practically  possible. 

Since  the  greater  number  of  bacteria  are  found  in  the 
lower  part  of  the  udder,  and  hence  in  the  first  milk  drawn 
from  each  teat,  it  is  the  custom  to  discard  the  fore-milk,  or 
the  first  few  streams  from  each  teat.  This  reduces  the 
number  of  bacteria  found  in  the  milk,  but  will  have  little, 
if  any,  influence  on  the  keeping  properties  of  the  milk,  since 
the  organisms  found  in  the  udder  grow  very  slowly  at  ordi- 
nary temperatures. 

Contamination  from  the  air. — The  air  in  a  stable  con- 
tains varying  numbers  of  bacteria  adherent  to  the  dust 
particles.  Some  of  the  manure  becomes  dry,  and  is  ground 
into  fine  particles  by  the  movements  of  the  cattle.  This  is 
supplemented  by  the  soil  that  is  brought  into  the  stable  on 
the  hoofs  of  the  cattle.  The  dry  feed  is  covered  with  dust 
and  minute  particles  of  soil;  the  bedding  and  coat  of  the 
cow  are  also  covered  with  dust.     Any  operation  that  serves 


140  AGRICULTURAL  BACTERIOLOGY 

to  throw  the  dust  from  these  sources  into  the  air  facilitates 
the  passage  of  some  of  it  into  the  milk.  The  particles  settle 
rapidly.  Therefore,  if  dust-raising  operations,  such  as 
bedding,  brushing  the  cattle,  and  feeding  dry  feed  are  car- 
ried out  some  time  before  the  milking-time,  the  contamina- 


Fig.  30.     Contamination  from  the  Air 

A  culture  plate  exposed  for  thirty  secouds  in  a  dusty  stable  shows  numerous 

colonies  of  bacteria   and  molds 

tion  of  the  milk  from  the  air  will  be  slight.  The  amount 
of  foreign  matter  introduced  into  the  milk  from  the  air  is 
very  small  compared  to  that  introduced  from  other  sources. 
The  types  of  microorganisms  found  in  the  air  are  not 
those  primarily  concerned  in  the  spoiling  of  milk.  The 
contamination  of  milk  from  the  air  is  therefore  relatively 
unimportant,  both  quantitatively  and  qualitatively.  Never- 
theless,   the    contamination    from    this    source    should    be 


CONTAMINATION  OP  FOODS  141 

avoided  as  far  as  practicable,  sincc«only  by  directing  atten- 
tion to  all  sources  of  contamination  can  the  bacterial  con- 
tent of  milk  be  kept  at  a  low  level. 

Contamination  from  the  animal. — The  larger  part  of 
foreign  matter  introduced  into  milk  comes  from  the  udder 
and  flanks  of  the  animal.    In  improperly  constructed  sta- 


Fig.  31.     Dirt  Tests 
A  pint  of  milk  was  passed  through  each  of  the  cotton  filters.     The  amount  of 
dirt  in  tlie   respective  samples  of  milk  is  shown  by  the  color  imparted  to  the 

cotton 

blcs,  and  where  the  bedding  is  not  sufficiently  abundant,  the 
flanks  often  become  coated  with  manure.  The  udder  may 
also  become  soiled.  If  the  yards  are  muddy,  if  the  cows 
have  access  to  mud-holes  or  muddy  streams,  the  udder  and 
teats  will  be  soiled.  Even  on  pasture  the  udder  becomes 
coated  with  dust. 

The  extent  of  the  contamination  from  the  animal  depends 
on  her  condition  as  to  cleanliness.  It  is  impossible  to  draw 
milk  from  a  dirty  animal  without  grossly  contaminating  it. 
The  farmer  can  not  afford  to  clean  soiled  animals  before 


142 


AGRICULTURAL  BACTERIOLOGY 


milking;  he  must  exert  his  efforts  to  prevent  the  soiling  of 
the  animal.  The  yards  should  be  well  drained,  and  covered, 
if  possible,  with  some  material  that  will  not  become  muddy, 
such  as  cinders  or  gravel. 

It  should  be  kept  in  mind  that  the  stable  in  which  dairy 
cattle  are  kept  represents  a  factor  in  the  determination  of 


Fig.  32.     Bacteria  on  Hairs 

Cow  hairs  were  placed  on  the  surface  of  an  agar  plate.     The  adherent  bacteria 

developed  and  formed  colonies 

the  quality  of  the  food  that  is  to  be  produced  therein.  The 
stalls  should  be  so  constructed  that  the  cows  will  automati- 
cally be  kept  clean.  They  should  be  of  a  proper  length  for 
each  animal,  and  the  gutters  should  be  deep  and  wide  in 
order  that  the  manure  that  accumulates  between  the  periods 
of  cleaning  will  not  reach  the  level  of  the  floor  of  the  stall. 


CONTAMINATION  OF  FOODS  143 

The  stable  should  be  cleaned  each  day;  and  an  ample  sup- 
ply of  bedding  should  be  provided  in  order  that  the  manure 
carried  on  to  the  stall  floor  by  the  animal  will  be  absorbed. 
The  beddinp:  should  be  of  such  a  nature  that  it  will  not  con- 
taminate   the    coat    of   the    animal.     Fresh,    clean    straw, 


Fig    33      A  Dirty  Stable 
It   is   impossible  to   |)rodiice  good   milk   in  such   an  environment 

shredded  corn  stover,  sawdust,  and  shavings  are  good  ab- 
sorbents, and  are  relatively  free  from  dust  and  bacteria. 
Moldy  or  rotten  straw  and  litter  from  the  horse  stalls  are 
objectionable  because  of  their  influence  on  the  quality  of  the 
milk.  Every  effort  should  be  made  to  keep  the  animal  in  a 
clean  condition,  since  this  is  one  of  the  ways  by  which  a 
great  deal  of  contamination  can  be  prevented  at  a  minimum 
of  expense. 
l*revention  of  contamination  from  the  animal. — Even 


144 


AGRICULTURAL  BACTERIOLOGY 


conta:\iination  op  foods  145 

under  the  best  of  conditions  in  both  sumraer  and  winter, 
the  coat  of  the  animal  will  become  dusty,  and  it  is  advisable 
to  remove  this  dust,  as  well  as  the  loose  hair,  before  milking. 
This  can  be  done  by  brushing  the  flanks  and  udder  shortly 
before  milking  time,  in  order  that  the  dust  thus  created  shall 
have  time  to  settlf^.     A  still  better  way  is  to  wipe  the  uddei* 


Fig    35.     Sanitary  Milk  Pails 

Tlio   Stadtmueller  and  the  Truman   pails  are   two  of  the  most  practical  of  tlic 

many   that  liave   l)een    devised 

with  a  clean,  damp  cloth.  To  avoid  most  completely  this 
source  of  contamination,  the  udder  should  be  washed,  and 
the  excess  water  removed  with  a  clean  cloth.  The  udder 
is  thus  left  damp  and  no  dust  can  leave  it.  The  latter 
method  is  the  one  used  on  farms  on  which  the  highest  grade 
of  milk  is  produced.  Clipping  the  udder  and  flanks  serves 
to  prevent  the  entrance  of  dust  from  the  animal,  and  to 
make  the  cleaning  of  a  soiled  animal  much  easier  than  if 
the  hair  is  long. 

The  exclusion  of  dirt  from  the  animal  may  also  be  at- 
tained l)y  the  use  of  a  small  topped  milk-pail,  in  which  the 
opening  is  restricted  in  some  way.  Such  pails  (Fig.  35) 
are  very  effective  in  the  exclusion  of  dirt,  and  are  nearly  as 
convenient  to  use  as  is  the  common  open  pail.     The  larger 


146  AGRICULTURAL  BACTERIOLOGY 

part  of  the  dirt  comes  from  the  flank  of  the  animal  rather 
than  from  the  udder.  The  milking-machine  is  also  an  effec- 
tive way  of  preventing  the  introduction  of  mud  and  dirt 
into  the  milk,  since  the  milk  passes  from  the  teat  directly 
into  tubes  that  lead  to  covered  pails.  The  effect  that  such 
factors  have  in  producing  clean  milk  is  dependent  on  the 
condition  of  the  coat  of  the  animal.  If  the  latter  is  very 
clean,  the  use  of  the  covered  pail  will  have  little,  if  any, 
influence  in  improving  the  quality  of  the  milk;  but  if  the 
animal  is  dirty,  the  influence  will  be  great.  The  extent  to 
which  any  producer  can  apply  methods  for  the  prevention 
of  the  contamination  of  milk  is  to  be  determined  by  the 
results  produced,  and  whether  he  can  obtain  compensation 
from  the  consumer  for  the  additional  expense  incurred. 
Common  decency,  however,  demands  that  the  introduction 
of  visible  quantities  of  mud  and  manure  be  avoided.  Pre- 
vention of  contamination  should  begin  with  those  operations 
that  will  have  the  maximum  effect. 

Influence  of  the  milker.— The  milker  should  appreciate 
the  relative  importance  of  the  various  sources  of  contami- 
nation, and  should  know  the  most  effective  means  of  pre- 
venting the  introduction  of  microorganisms.  The  dress  and 
hands  of  the  milker  should  be  clean,  and  the  methods  of 
milking  such  as  to  avoid  contamination.  Milking  should 
not  be  done  with  wet  hands.  If  the  conditions  demand 
something  to  soften  the  teats,  vaseline  may  be  used.  The 
whole  hand  should  be  used  in  milking,  rather  than  stripping 
with  the  thumb,  and  forefinger. 

Contamination  from  the  utensils. — It  is  difficult  to  clean 
dirty  utensils  with  sufficient  thoroughness  to  remove  all 
traces  of  organic  matter  to  the  extent  that  bacterial  growth 
will  not  take  place  in  case  the  temperature  and  moisture 
conditions  permit.  The  thoroughness  with  which  the  uten- 
sil can  be  cleaned  is  dependent  on  the  material  of  whicl/ 


CONTAI\IINATION  OF  FOODS  147 

it  is  made.  Woodenware  can  be  cleaned  less  easily  and  less 
thoroughly  than  can  metal  vessels.  Again,  if  the  utensil  is 
so  constructed  that  joints  and  angles  exist  which  can  not  be 
readily  reached  in  the  cleaning  by  the  cloth  or  brush,  it  will 
be  difficult  to  remove  accumulations  of  organic  matter.  The 
sharp  angles  encountered  in  milk-cans,  and  the  open  joints 
that  are  found  in  the  cheaper  grades  of  tinware,  make  such 
utensils  difficult  to  clean. 

The  condition  of  the  utensil  is  another  factor  that  deter- 
mines the  ease  with  which  the  cleaning  process  is  carried 
out.  The  smooth  surface  of  a  new  tin  vessel  is  much  .easier 
to  clean  than  that  of  a  rusted  and  dented  utensil.  Such 
complicated  utensils  as  milking-machines  and  cream-sepa- 
rators are  difficult  to  keep  in  a  sanitary  condition.  The 
rubber  tubes  that  conduct  the  milk  from  the  teat-cups  to 
the  receiving  can  of  the  machine  can  not  be  entirely  freed 
from  milk,  and  it  is  impossible  to  dry  them.  In  order  to 
avoid  a  large  amount  of  contamination  from  the  tubes,  it  is 
necessary  to  place  them  in  an  antiseptic  solution  in  such  a 
manner  that  they  shall  be  entirely  filled  with  the  solution 
and  not  partially  filled  with  entrapped  air.  No  solution 
has  been  found  entirely  satisfactory.  If  a  few  pieces  of 
fresh  quick  or  stone  lime  are  kept  in  the  tank  in  which  the 
rubber  parts  of  the  machine  are  to  be  placed,  the  alkalinity 
of  the  solution  will  be  such  as  to  prevent  bacterial  growth. 
A  saturated  solution  of  common  salt  may  also  be  used,  but 
this  will  not  completely  prevent  the  growth  of  bacteria. 
Certain  kinds  will  grow  very  slowly  therein. 

The  addition  of  a  small  amount  of  a  solution  of  calcium 
hypochlorite  or  bleaching  powder  to  the  brine  will  destroy 
the  bacteria.  The  addition  of  one  part  of  a  solution  ob- 
tained by  stirring  one  pound  of  bleaching  powder  in  one 
gallon  of  water,  and  allowing  the  insoluble  portion  to  settle, 
to  two  hundred  parts  of  the  brine  at  semi-weekly  intervals, 


148  AGRICULTURAL  BACTERIOLOGY 

will  suffice  to  keep  the  tubes  in  good  condition.  The  action 
of  the  solution  must  be  supplemented  by  a  thorough  clean- 
ing of  the  parts  each  week.  As  the  tubes  are  used,  minute 
cracks  form  on  the  inner  surface  and  become  filled  with 
milk.  The  antiseptic  solution  enters  them  slowly,  and  the 
bacterial  growth  that  may  occur  therein  will  be  forced  out 
of  the  cracks  under  the  influence  of  the  constantly  chang- 
ing pressure  in  the  tubes  when  the  machine  is  in  use. 

The  tubes  may  also  be  kept  in  a  satisfactory  sanitary 
condition  by  placing  them  in  water  and  heating  to  176°  F. 
for  a  .few  minutes.  The  tubes  may  be  allowed  to  remain  in 
the  water  until  they  are  to  be  used  again. 

Cleaning  of  milk  utensils.— Milk  utensils  shoul(l  be 
washed  as  soon  as  possible  after  using,  for  if  the  milk  is 
allowed  to  dry  on  the  surface  of  the  utensils  it  is  difficult 
to  remove.  They  should  be  rinsed  with  cold  water,  then 
washed  with  a  hot  solution  of  a  washing  powder.  Soaps 
and  soap  powders  are  difficult  to  remove  by  rinsing,  and  are 
not  as  effective  in  the  removal  of  milk  and  grease  as  are 
washing  powders.  A  stiff  brush  should  be  used  for  scrub- 
bing, for  much  of  the  dirt  can  be  removed  only  by  me- 
chanical force.  Finally,  the  vessel  should  be  rinsed  with 
boiling  water,  using  it  in  such  quantities  that  the  vessel  will 
be  heated  sufficiently,  so  that  rapid  and  complete  drying 
will  take  place.  The  growth  of  microorganisms  can  not 
occur  in  the  absence  of  water.  Imperfect  washing  will  not 
be  so  serious,  if  the  utensil  is  perfectly  dried,  as  will  a  more 
thorough  washing  with  imperfect  drying.  If  steam  is 
available,  the  utensils  can  be  so  thoroughly  heated  as  to 
destroy  all  organisms  that  are  likely  to  injure  the  keeping 
quality  of  the  milk.  Furthermore,  steaming  facilitates  the 
drying  process.  In  the  washing-rooms  of  city  milk  depots, 
can  driers  form  an  important  part  of  the  equipment.  The 
amount  of  bacterial  growth  that  can  take  place  in  a  few 


CONTAMINATION  OF  FOODS  140 

cubic  centimeters  of  water  in  a  milk  utensil  is  often  suffi- 
cient to  add  as  many  as  50,000  bacteria  to  each  cubic  centi- 
meter of  the  milk  when  the  utensil  is  filled.  It  is  doubtful 
whether  such  a  number  of  bacteria  are  ever  added  to  the 
milk  throu<;h  the  introduction  of  dirt. 

All  utensils  should  be  washed  after  each  period  of  use. 
This  is  especially  true  of  cream-separators.  It  is  impos- 
sible to  remove  Ihe  accumulation  of  organic  matter  that 
collects  on  the  wall  of  the  bowl  by  running  water  through 
the  machine.  It  is  essential  that  the  machine  be  taken 
apart,  well  washed,  and  thoroughly  dried.  Strainer  cloths 
sliould  l)e  washed  as  free  from  milk  as  possible,  and  placed 
where  they  will  dr}'  quickly,  so  that  no  growth  can  occur 
in  tluMii. 

Contamination  from  factory  by-products. — The  cans  in 
which  milk  is  transported  to  the  creamery  and  cheese  fac- 
tory are  also  used  to  carry  the  whey  and  skim  milk  back  to 
the  farm.  This  custom  would  have  no  disadvantage  if  the 
cans  were  thoroughly  washed  before  being  used  again. 
This,  however,  is  the  exception  rather  than  the  rule,  and 
hence  bacteria  find  their  way  from  the  whey -tank  to  the 
cheese-vat.  The  great  opportunity  for  the  whey-tank  to 
become  seeded  with  harmful  types  of  bacteria  or  yeasts 
makes  this  source  of  contamination  of  much  importance  in 
the  manufacture  of  cheese.  Such  trouble  can  be  avoided  by 
heating  the  whey  to  a  temperature  of  140°  to  155°  F.  as  it 
passes  from  the  cheese-vat  to  the  whey-tank,  where  it  is 
stored  until  the  following  day.  If  the  volume  of  whey  is 
large,  it  will  require  considerable  time  for  the  temperature 
to  fall  to  a  point  where  any  bacterial  growth  can  take  place. 
Heating  to  the  above  temperature  is  sufficient  to  destroy 
most  non-spore-forming  bacteria.  Whey  so  treated  will  be 
sweet  when  returned  to  the  farm,  and  will  have  a  higher 
feeding  value  than  sour  whey.     It  will  also  be  free  from 


150  AGRICULTURAL  BACTERIOLOGY 

disease-producing  organisms  that  may  thus  be  carried  from 
one  farm  to  another.  It  has  been  found  that  the  enhanced 
value  of  the  butter  and  cheese  is  more  than  sufficient  to  pay 
for  all  cost  of  treatment. 

Factors  determining  the  number  of  bacteria.— The  bac- 
terial content  of  any  sample  of  milk  is  dependent  on  the 
number  that  have  been  introduced  into  it  from  the  various 
sources  that  have  been  considered,  and  on  the  extent  to 
which  the  bacteria  have  grown  in  the  milk.  It  has  been 
shown  that,  under  ordinary  conditions,  the  utensil  is  the 
most  important  source  of  contamination,  and  the  animal  the 
next  in  importance.  Even  the  most  simple  utensil  that  is 
apparently  in  a  satisfactory  condition  may  add  an  unbe- 
lievable number  of  bacteria  to  the  milk. 

In  seeking  to  improve  the  quality  of  milk  from  the  stand- 
point of  contamination  with  bacteria,  the  utensils  should 
be  considered  first.  Prevention  of  growth  therein  by  the 
complete  removal  of  water  should  take  precedence  over  at- 
tempts to  sterilize  the  utensils  by  steam,  unless  the  steam- 
ing can  be  so  prolonged  that  the  utensil  will  dry  quickly 
from  the  heat  imparted  to  it.  Steaming  for  a  few  seconds, 
and  leaving  the  utensil  in  a  moist  condition,  defeats  the 
aim  in  view.  Utensils  in  which  no  bacterial  growth  has 
taken  place,  supplemented  by  wiping  off  the  visible  accumu- 
lations of  mud  and  manure  from  the  udders  of  the  cows,  and 
the  use  of  small-topped  pails,  will  prevent  the  entrance  of 
the  major  portion  of  organisms  into  the  milk. 

The  problem  connected  with  the  second  factor,  that  of 
the  growth  of  bacteria  in  milk,  must  be  solved  by  means  to 
be  treated  in  a  subsequent  chapter.  A  high  bacterial  con- 
tent does  not  necessarily  mean  a  milk  produced  under  un- 
desirable conditions  with  reference  to  cleanliness,  but  it 
does  imply  a  milk  of  undesirable  quality  from  the  stand- 
point of  the  consumer. 


CONTAMINATION  OF  FOODS  151 

Straining"  and  clarifying  milk. — It  might  be  thought  that 
the  forei<i:n  matter  introduced  into  milk  could  be  removed, 
thus  reducing  the  bacterial  content  as  well.  P^'or  the  re- 
moval of  dirt,  straining  the  milk  is  generally  resorted  to. 
This  practice  may  be  carried  out  so  as  to  remove  the  in- 
soluble material  that  has  found  its  way  into  milk,  but  it 
will  have  little  if  any  influence  on  the  reduction  of  bac- 
teria, since  they  are  readily  washed  off  from  the  surface 
of  solid  matter,  and  are  able  to  pass  the  pores  of  the  finest 
strainer  that  may  be  used.  All  processes  of  straining  can 
serve  only  to  improve  the  appearance  of  the  milk,  but  can 
have  little  if  any  influence  on  its  keeping  quality  or  health- 
fulness. 

Much  of  the  milk  now  sold  in  cities  is  subjected  to  a  proc- 
ess known  as  clarification  by  passing  it  through  a  machine 
that  is  comparable  to  a  cream-separator.  The  insoluble 
material  that  has  been  introduced  into  the  milk  will  be 
completely  removed  by  the  strong  centrifugal  force  ap- 
plied to  the  milk  in  the  rapidly  revolving  bowl  of  the  clari- 
fier.  This  material  will  be  supplemented  by  cellular  ele- 
ments from  the  udder,  and  by  casein,  the  whole  forming 
a  slimy  mass  known  as  separator  slime.  The  color  is  white 
if  the  milk  treated  is  relatively  free  from  dirt.  Usually  it 
is  grayish  in  color,  because  of  the  dirt  therein.  Since  the 
bacterial  content  of  the  slime  is  much  higher  than  that  of 
the  untreated  milk,  the  process  serves  to  remove  a  portion 
of  the  bacteria  from  the  milk.  The  actual  reduction  is, 
however,  so  small  as  to  be  of  no  practical  importance  in 
influencing  the  keeping  quality  or  the  healthfulness  of  the 
milk.  Like  straining,  it  improves  only  the  appearance  of 
the  product. 

Influence  of  feed  on  contamination  of  milk.— The  bac- 
terial content  of  the  feed  or  water  consumed  by  the  cow 
can  not  have  a  direct  influence  on  the  kinds  or  number  of 


152  AGRICULTURAL  BACTERIOLOGY 

bacteria  that  are  introduced  into  the  milk,  as  these  organ- 
isms do  not  pass  from  the  intestine  through  the  blood  and 
appear  in  the  milk  directly.  They  may,  however,  have  an 
indirect  intluence  by  changing  the  type  of  the  bacterial 
flora  in  the  manure,  some  of  which  nearly  always  finds  its 
way  into  the  milk  from  the  dirty  flanks  of  the  animal.  If 
the  feed  is  such  as  to  make  the  manure  more  liquid  than 
usual,  it  is  more  difficult  to  keep  the  animals  clean. 

The  use  of  improper  feed  may,  however,  alter  the  taste 
of  the  milk  or  its  value  as  food.  Cabbage,  turnips,  rape, 
wild  onions,  and  some  weeds  that  may  be  eaten  in  the  pas- 
ture contain  certain  volatile  principles  which  are  absorbed 
directly  into  the  circulation  and.  may  then  appear  in  the 
milk,  just  as  the  odor  of  onions  appears  in  the  exhaled 
breath.  Where  such  substances  are  eliminated  in  the  milk, 
the  normal  taste  is  changed.  This,  of  course,  does  not  in- 
jure the  healthfulness  of  the  milk,  but  it  decreases  its  com- 
mercial value.  Certain  drugs,  as  mercury,  arsenic,  or 
strychnine,  if  given  to  cows,  may  be  eliminated  with  the 
milk.  The  milk  of  an  animal  receiving  medicine  should 
not  be  used  for  human  food,  and  especially  for  the  feeding 
of  children.  Fats  readily  absorb  any  odors  with  which 
they  come  in  contact,  and  milk,  by  reason  of  its  cream 
content,  thus  absorbs  some  odors,  such  as  that  of  bananas, 
with  especial  avidity.  In  order  not  to  injure  the  flavor 
of  the  milk,  it  should  be  kept  and  handled  in  an  atmos- 
phere that  is  free  from  odors  of  all  kinds.  These  absorbed 
odors  are  often  difficult  to  differentiate  from  those  due  to 
the  growth  of  bacteria  in  the  milk. 

Contamination  of  other  foods  than  milk. — There  are  few 
foods  that  are  handled  in  such  a  condition  as  to  make  them 
comparable  to  milk.  Most  of  them  are  protected  from  the 
invasion  of  microorganisms.  Others,  while  subject  to  con- 
tamination, do  not  permit  the  growth  of  the  organisms  that 


CONTAMINATION  OF  FOODS  153 

come  in  contact  with  them.  There  are  two  important  ex- 
amples that  are  quite  comparable  to  milk  in  every  respect. 
Oysters  can  not  be  subjected  to  any  preservative  agent 
other  than  cold.  They  are  constantly  exposed  to  contami- 
nation, and  form  an  ideal  medium  for  many  bacteria.  The 
water  in  which  the  oyster  is  grown  supplies  the  initial  con- 
tamination. They  are  commonly  immersed  in  fresh  water 
for  a  short  period  for  the  purpose  of  ''plumping."  The 
streams  in  which  they  are  placed  are  often  contaminated 
with  sewage.  A  contamination  with  both  saprophytic  and 
pathogenic  bacteria  is  thus  possible.  In  opening  the  shells, 
the  oyster  is  exposed  to  contamination  from  the  hands  of 
the  worker,  and  the  utensils  also  serve  to  add  their  quota 
of  bacteria.  The  juice  of  the  oyster  is  rich  in  protein  and 
neutral  in  reaction,  supplying  an  ideal  environment  for  the 
growth  of  putrefactive  bacteria. 

Chopped  meats  present  similar  problems.  In  their  prep- 
aration the  bacteria  are  uniformly  mixed  with  them.  Food 
and  moisture  are  abundant.  Spoilage  quickly  occurs  un- 
less the  bacteria  are  restrained  in  their  development. 

Contamination  of  foods  is  not  confined  to  the  handling 
they  receive  in  the  channels  of  commerce,  but  occurs  in  the 
home.  Unused  portions  of  food  left  over  from  the  day's 
meal  are  peculiarly  liable  to  bacterial  activity.  The  con- 
tamination in  the  home  is  largely  from  utensils,  the  ade- 
quate sterilization  and  drying  of  which  will  do  much  to 
enhance  the  keeping  of  food  from  one  day  to  another. 

It  is  essential  that  all  foods  that  must  be  used  without 
previous  cleaning,  and  especially  those  that  are  eaten  with- 
out cooking,  be  protected  from  contamination,  both  for 
esthetic  and  sanitary  reasons.  Bakery  goods,  candies,  etc., 
should  be  handled  with  due  regard  to  cleanliness.  Dust 
contamination  and  pollution  incident  to  handling  food 
products  are  especially  to  be  considered. 


CHAPTER  XIV 

THE  CONTAMINATION  OF  FOODS  WITH 
PATHOGENIC  BACTERIA 

The  diseases  of  man  and  the  lower  animals  that  are  due 
to  the  growth  of  microorganisms  in  the  body  of  the  living 
animal  are  propagated  by  the  passage  of  the  organism  from 
the  body  of  the  diseased  individual  into  the  body  of  a  still 
healthy  individual.  Many  diseases  are  transmitted  only  by 
very  direct  contact  of  the  healthy  with  the  diseased.  With 
others  the  organism  may  be  transported  over  long  distances 
in  time  and  space.  Many  objects  may  serve  as  transport- 
ing agents.     Prominent  among  them  are  certain  foods. 

The  causal  organisms  are  usually  contained  in  some  of 
the  discharges  of  the  body,  which  in  one  way  or  another 
come  in  contact  with  food  materials.  Frequently  the  or- 
ganisms are  not  resistant  to  desiccation,  and  in  this  case 
can  not  be  distributed  on  dry  solid  objects,  but  may  be  car- 
ried by  moist  foods  such  as  milk  and  water.  There  are  a 
number  of  reasons  why  these  foods  are  especially  important 
in  the  causation  of  disease.  In  the  case  of  milk,  the  prod- 
uct of  many  farms  is  brought  together  and  mixed  in  the 
plant  of  the  milk  distributor.  A  contamination  of  the 
product  on  any  one  farm  may  thus  result  in  the  introduc- 
tion of  the  harmful  organism  into  hundreds  of  city  homes. 
The  original  contamination  may  be  slight,  but  by  the  time 
the  milk  is  consumed,  it  may  contain  an  innumerable  num- 
ber of  the  organisms;  for  certain  of  the  pathogenic  bac- 
teria find  in  milk  a  favorable  nutrient  medium,  and  can 
grow  at  the  temperatures  at  which  it  is  often  stored.     There 

154 


TUBERCULOSIS  155 

is  opportunity  for  milk  to  serve  as  a  transporting  agent  of 
.disease-producing  organisms  from  the  farm  to  the  city,  not 
at  infrequent  intervals,  but  daily  throughout  the  year. 
The  milk  is  subject  to  contamination  with  the  organisms 
causing  disease  in  the  milk-producing  animal,  and  also  with 
those  of  man.  Man  is  susceptible  to  a  number  of  diseases 
that  primarily  affect  cattle.  These  facts  place  milk  first 
among  the  inanimate  objects  in  the  distribution  of  disease. 
The  diseases  most  often  spread  by  milk  are  tuberculosis, 
typhoid  fever,  diphtheria,  and  scarlet  fever.  Some  idea 
of  the  importance  of  milk  as  an  agent  in  the  distribution  of 
disease  is  shown  in  the  following  summary  of  epidemics 
that  were  traced  to  milk  in  Boston  in  the  interval  1907  to 
1911. 

1907  Diphtheria    72  cases 

1907  Scarlet  Fever 717  cases 

1908  Typhoid   Fever    400  cases 

1910  Scarlet  Fever 842  cases 

1911  Tonsilitis 2,064  cases 

Water  is  probably  to  be  classed  as  second  in  importance 
to  milk  in  the  distribution  of  disease-producing  organisms. 
While  some  disease  organisms  can  live  in  water  for  a  vary- 
ing period  of  time,  this  medium  does  not  offer  the  oppor- 
tunity for  actual  growth  that  milk  does.  Typhoid  fever 
is  the  principal  disease  that  is  water-borne. 

Bovine  tuberculosis. — A  detailed  discussion  of  this  dis- 
ease will  be  presented  in  a  subsequent  chapter.  Only  the 
facts  relevant  to  the  relation  of  the  disease  in  cattle  to  tu- 
berculosis in  man  will  be  presented  here.  Tuberculosis  is 
a  disease  that  affects  many  portions  of  the  body.  It  is 
characterized  by  the  formation  of  nodules  or  tubercles, 
which  gradually  increase  in  size,  giving  rise  to  abscesses, 
the  contents  of  which  contain  the  tubercle  bacilli.     When 


156  AGRICULTURAL  BACTERIOLOGY 

these  abscesses  are  located  in  parts  of  the  body  from  which 
the  bacilli  may  escape  to  the  exterior  on  the  breaking  of, 
the  abscesses,  the  disease  is  said  to  be  of  the  open  type. 
This  stage  in  the  progress  of  the  disease  is  not  reached  for 
a  considerable  number  of  months,  or  even  years,  after  the 
inception  of  the  disease.  Approximately  25  per  cent,  of 
tubercular  cattle  have  the  open  form  of  the  disease. 
The  milk  of  such  animals  is  likely  to  be  contaminated  with 
the  organism,  the  frequency  and  extent  of  the  contamina- 
tion depending  upon  the  location  of  the  abscesses.  They 
may  be  present  in  the  udder,  in  which  case  the  milk  is 
almost  sure  to  be  contaminated.  If  the  abscesses  are  lo- 
cated in  the  lungs,  as  is  most  commonly  the  case,  the  in- 
fectious material  will  be  coughed  up  from  the  lungs ;  a  por- 
tion is  ejected  from  the  mouth,  while  the  remainder  is 
swallowed.  The  tubercle  bacilli  therein  are  not  destroyed 
in  their  passage  through  the  alimentary  tract,  and  are 
eliminated  in  the  feces.  Since  some  fecal  matter  inevitably 
finds  its  way  into  milk,  the  opportunity  is  offered  for  con- 
tamination of  the  milk  with  tubercle  bacilli  coming  from 
the  lungs.  Abscesses  in  the  intestine  or  liver  may  serve  to 
contaminate  the  milk  in  the  same  manner. 

Tubercular  abscesses  in  the  udder  may  discharge  their 
contents  directly  into  the  milk-ducts.  The  extent  of  con- 
tamination from  the  udder  is  much  greater  than  from  other 
sources,  and  is  probably  of  much  greater  importance;  but 
it  is  probably  less  frequent  than  contamination  from  the 
lungs,  either  by  means  of  the  manure  or  the  dust  of  the 
stable. 

The  percentage  of  milch-cows  suffering  from  tuberculosis 
varies  widely  in  different  parts  of  the  world,  but  it  is  defi- 
nitely appreciable  in  all  sections  where  dairy  development 
has  been  considerable.     It  is  probable  that  mixed  milk  sup- 


TUBERCULOSIS  157 

plies,  such  as  those  represented  by  the  supplies  of  the 
larger  cities,  constantly  contain  tubercle  bacilli  to  some  ex- 
tent. The  dilution  of  the  milk  of  diseased  animals  with 
that  of  healthy  animals  tends  to  diminish  the  danger,  both 
to  animals  and  to  human  beings  consuming  such  milk. 
The  alarming  extent  of  tuberculosis  in  hogs  Ls  direct  evi- 
dence of  the  constant  and  marked  contamination  of  the 
mixed  milk. 

It  is  impossible  to  examine  market  milk  in  any  effective 
manner  for  the  presence  of  tubercle  bacilli  in  order  to  de- 
termine whether  an  animal  is  eliminating  the  organisms; 
hence,  under  practical  conditions,  it  is  necessary  to  consider 
any  animal  that  has  the  disease  as  a  potential  source  of 
danger,  although  she  may  not  be  giving  off  the  organisms. 
The  usual  method  of  preventing  the  contamination  of  the 
milk  with  bovine  tubercle  bacilli  is  to  apply  the  tuberculin 
test  to  the  animals,  and  to  remove  all  animals  that  react  to 
the  test. 

The  importance  of  bovine  tuberculosis  as  a  factor  in  the 
occurrence  of  the  disease  in  man  has  been  established  only 
within  the  last  few  years.  Through  detailed  studies  made 
on  organisms  isolated  from  fatal  cases  of  the  disease  in 
people  of  all  ages,  it  has  been  possible  to  ascertain  whether 
the  organism  in  question  belonged  to  the  human  or  the 
bovine  type.  The  organism  from  cattle  is  more  virulent  for 
most  experimental  animals  than  is  the  organism  from  man. 
This,  together  with  the  differences  in  growth  on  culture 
media,  enables  the  bacteriologist  to  tell  whether  the  organ- 
ism originally  came  from  cattle  or  from  man. 

From  the  data  that  have  been  collected  in  various  parts 
of  the  world,  it  is  certain  that  bovine  tuberculosis  is  re- 
sponsible for  a  portion  of  this  disease  in  man.  The  sus- 
ceptibility to  infection  from  contaminated  milk  is  greatest 


158  AGRICULTURAL  BACTERIOLOGY 

in  the  case  of  the  young.  The  bovine  tubercle  bacillus  has 
been  found  but  infrequently,  as  compared  to  the  human 
tubercle  bacillus,  in  people  over  sixteen  years  of  age. 

The.  organisms  are  able  to  penetrate  the  tissues  of  the 
throat,  especially  the  tonsils,  from  which  they  pass  to  the 
lymph-glands  of  the  neck.  The  bacilli  may  also  pass 
through  the  intestinal  wall,  producing  tuberculosis  of  the 
abdominal  cavity.  The  methods  for  safeguarding  the 
wholesomeness  of  milk  will  be  discussed  in  connection  with 
methods  used  to  preserve  it. 

Septic  sore  throat  and  garget. — Inflammation  of  the 
udder  is  of  frequent  occurrence  in  cattle.  The  more  seri- 
ous cases  are  due  to  the  invasion  of  the  udder  by  bacteria, 
the  development  of  which  is  not  restrained  by  the  germi- 
cidal action  of  the  fluids  of  the  udder.  A  considerable 
number  of  kinds  of  bacteria  have  been  found  associated 
with  such  troubles.  It  is  probable  that  the  majority  of 
them  are  incapable  of  causing  harm  in  persons  consuming 
the  milk.  A  more  serious  form  of  garget  is  believed  to  be 
due  to  organisms  that  come  from  cases  of  septic  sore  throat 
in  man.  It  is  supposed  that  the  contaminated  hands  of  the 
milker  serve  to  carry  the  bacteria  on  to  the  teats.  They 
invade  the  udder  through  the  milk  ducts.  The  inflamma- 
tion caused  by  their  presence  may  be  so  slight  as  not  to  at- 
tract attention,  and  yet  the  milk  may  produce  widespread 
epidemics  of  throat  trouble.  All  cases  of  udder  inflamma- 
tion should  be  considered  as  potentially  dangerous,  and  the 
milk  rejected. 

In  the  case  of  certain  diseases  of  milk-producing  animals 
the  organism  is  present  in  the  milk  at  the  time  of  its  with- 
drawal from  the  udder,  not  only  from  animals  that  have 
the  disease  but  from  animals  that  are  apparently  in  normal 
health.  Malta  fever,  a  disease  of  goats,  and  contagious 
abortion  of  cattle,  are  examples.     In  the  case  of  the  latter 


SEPTIC  SORE  THROAT  159 

it  is  known  that  an  animal  may  continue  to  excrete  the 
bacilli  for  j-ears.  It  is  not  known  that  the  organism  is  of 
any  sanitary  importance,  as  far  as  man  is  concerned,  but 
undoubtedly  such  animals  are  the  cause  of  the  spread  of 
the  disease  to  other  individuals.  The  disease  is  often 
spread  by  purchase  of  affected  stock. 

In  a  general  way  it  may  be  said  that  the  milk  of  an  animal 
that  is  suffering  from  any  disease  whatever  should  not  be 
used  for  human  food.  It  maj^  not  be  true  that  the  milk 
would  be  distinctly  harmful,  but  it  is  always  well  to  err  on 
the  safe  side.  Such  troubles  as  abscesses  on  any  part  of 
the  body,  inflammation  of  the  intestines,  or  any  abnormal 
condition  after  calving  should  cause  the  rejection  of  the 
milk. 

Typhoid  fever.— Of  those  diseases  that  do  not  affect  cat- 
tle, but  are  spread  by  means  of  milk,  typhoid  fever  is  the 
most  important.  The  organisms  producing  the  disease  en- 
ter the  body  with  the  food  or  drink.  They  establish  them- 
selves in  the  intestines,  and  from  there  penetrate  to  other 
parts  of  the  body.  They  are  eliminated  in  the  feces  and 
the  urine.  From  these  infectious  materials  they  are 
brought  in  contact  with  food  and  drink  by  a  number  of 
agents. 

Not  only  milk,  but  many  other  foods  and  water  are  con- 
cerned in  the  spread  of  typhoid  fever.  The  methods  by 
which  food  products  may  become  contaminated  are  so  simi- 
lar that  all  may  be  discussed  together.  Milk  has  one 
peculiarity  that  is  not  common  to  most  other  foods,  in  that 
the  typhoid  bacilli  find  in  it  an  excellent  culture  medium; 
and  since  growth  can  take  place  at  temperatures  far  below 
that  of  the  human  body,  indeed  at  temperatures  at  which 
milk  is  often  stored,  the  slight  contamination  that  might  be 
of  small  importance  in  other  foods  may  be  the  starting  point 
of  a  great  epidemic  when  milk  is  concerned.     The  typhoid 


160 


AGRICULTUKAL  BACTERIOLOGY 


Fig.   36.     Typhoid  Fever   Spread  by  Milk    (Stamford,   Conn.) 
The   small   squares    represent   milk    producers    and    dealers    and    the    lines    milk 
routes    in    a    village.     Three    hundred    and    eighty-six    cases    of    typhoid    fever 
occurred    on   one    route    and    but    eighteen    on    the   routes    of    the    other    nine 

distributors 

organism  is  unable  to  grow  in  water,  the  bacilli  gradually 
die,  and  within  a  week  or  ten  days  all  have  perished. 

Contamination  of  water  supplies.— The  most  frequent 
manner  in  which  water  is  contaminated  is  by  its  pollution 


SEPTIC  SORE  THROAT 


161 


with  sewage  containing  the  organism.  The  methods  of  dis- 
posal of  both  municipal  and  farm  sewage  often  are  such 
as  to  permit  of  its  introduction  into  the  water.  Munici- 
palities often  draw  their  water  supplies  from  a  body  of 
water  that  is  contaminated  by  sewage.  In  individual  sup- 
plies, the  farm  well  is  often  located  in  close  proximity  to 
the  outhouse,  and  if  the  well  is  not  protected  from  the 


Fig.  37.     Typhoid  Fever  Spread  by  Water 

The  entrance  of  infectious  material  into  a  cesspool  is  likely  to  contaminate  the 
well   unless   it  is  some  distance   from  the   cesspool 

entrance  of  surface  water,  or  seepage  from  the  upper  soil 
layers,  infectious  material  may  be  carried  into  the  well  by 
the  drainage  water.  If  the  well  is  a  drilled  one,  the  iron 
casing  should  extend  to  an  impervious  layer  of  soil  or  rock, 
and  the  curb  should  be  constructed  so  that  no  waste  water 
can  find  its  way  into  the  well.  If  the  well  is  dug  instead  of 
drilled,  the  upper  portion  of  the  protecting  wall  should  be 
laid  in  concrete,  and  the  surface  properly  protected  by  a 
concrete  curb. 

No  definite  statements  can  be  made  as  to  the  distance  in- 
fectious material  may  be  carried  by  the  drainage  water,  as 
this  depends  much  on  the  porosity  of  the  soil.  If  the  soil  is 
clay,  gravel,  or  sand,  the  movement  of  infectious  matter  will 
be  for  only  a  short  distance ;  but  if  the  soil  is  underlaid  with 
limestone,  underground  channels  may  develop  by  the  solu- 


162 


AGRICULTURAL  BACTERIOLOGY 


tion  of  the  limestone,  which  may  carry  the  organisms  for 
considerable  distances.  The  well  should  not  be  less  than 
one  hundred  feet  from  any  possible  source  of  pollution. 


1  Ti^t  Manho/e 


DOS'.  W£LI_  AOEOUflTEL-V  PROrTECTEO 

RGfliNST  v5utv7^cE.Co^^rwM^NAnoN 


Fig.  38.     Protection  of  a  Well 
All  wells  should  be  protected  from  surface  water  since  this  may  carry  disease- 
producing  organisms 

The  chief  protection  is  to  be  found  in  the  filtering  effect 
of  the  soil.  If  no  water  can  enter  the  well  until  it  has  first 
passed  through  at  least  fifteen  to  twenty  feet  of  soil,  there 
will  be  little  danger  of  infection. 

There  are  many  ways  in  which  contaminated  water  may 
come  in  contact  with  milk,  as  in  the  case  of  rinsing  the 


SEPTIC  SORE  THROAT  163 

milk  utensils  with  cold  water,  and  the  accidental  or  inten- 
tional addition  of  water  to  milk. 

The  protection  of  the  farm  water  supply  against  contam- 
ination with  typhoid  bacilli  is  important,  not  only  from  the 
standpoint  of  the  health  of  the  farm  home  itself,  but  also 
from  the  point  of  view  of  the  homes  to  which  the  products 
of  the  farm  find  their  way.  Milk  is  the  most  important 
product  in  this  regard,  because  the  typhoid  organism  can 
grow  so  luxuriantly  in  it,  and  because  so  large  a  proportion 
is  used  without  previous  heating. 

Springs  are  the  outlets  of  underground  streams.  Spring 
water  is  usually  free  from  bacteria  when  it  issues  from  the 
ground,  but  it  immediately  becomes  seeded  with  organisms 
from  contact  with  the  organic  matter  in  the  soil,  unless 
special  precautions  are  taken  to  guard  it. 

Contamination  from  typhoid  patients. — Direct  infection 
of  milk  sometimes  occurs  where  a  person  in  contact  with 
a  typhoid  case,  as  a  nurse,  also  is  concerned  with  the  prep- 
aration of  food  or  the  handling  of  milk.  Such  infection 
can  occur  only  when  carelessness  obtains  with  reference  to 
the  cleansing  of  the  hands  after  handling  the  patient.  In 
these  days  physicians  give  strict  directions  that  all  the  dis- 
charges of  a  typhoid  patient  shall  be  treated  with  a  disin- 
fectant that  will  destroy  the  typhoid  bacilli ;  but  if  care  is 
not  taken  by  those  coming  in  contact  with  the  patient,  they 
may  not  only  acquire  the  disease  themselves,  but  may  serve 
to  spread  it  to  others.  The  recognized  case  of  typhoid  is 
not  so  dangerous  as  those  that  are  not  clinically  apparent, 
such  as  mild  eases  for  the  treatment  of  which  no  physician 
is  consulted.  The  attack  may  be  so  slight  that  the  individ- 
ual may  not  be  aware  of  any  appreciable  illness.  Yet  the 
virulent  organism  is  eliminated  in  these  cases  to  the  same 
extent  as  in  pronounced  cases. 

Typhoid  carriers. — When  recovery  from  typhoid  takes 


164  AGRICULTURAL  BACTERIOLOGY 

place,  the  bacilli  usually  disappear  from  the  body,  but  in 
about  4  per  cent,  of  cases  the  organisms  persist  for  a  period 
of  time.  Exceptional  cases  have  been  recorded  in  which 
the  organisms  were  eliminated  for  many  years  after  re- 
covery. Such  people  are  known  as  typhoid  carriers.  It  is 
estimated  that  about  one  in  each  thousand  of  the  population 
is  to  be  classed  as  a  typhoid  carrier.  Whenever  such  a 
carrier  is  engaged  in  the  preparation  or  handling  of  food, 
an  epidemic  of  typhoid  may  result.  An  outbreak  of  four 
hundred  cases  in  New  York  city  was  traced  to  a  person  who 
had  had  the  disease  forty-seven  years  before.  As  has  been 
stated,  the  contamination  of  milk  is  important,  due  to  the 
opportunity  for  the  growth  of  the  bacilli ;  but  any  food  may 
become  contaminated  and  thus  become  the  cause  of  trouble. 
Since  no  one  recognizes  the  typhoid  carrier  as  such,  and 
since  generally  he  does  not  even  know  his  own  condition,  the 
problem  of  protecting  the  public  against  this  source  of 
typhoid  fever  seems  to  the  modern  health  officer  impossible 
of  solution. 

Oysters  and  typhoid  fever. — Shell-fish  represent  another 
food  that  is  not  infrequently  concerned  in  the  spread  of 
typhoid  fever.  When  oysters  are  removed  from  the  salt 
water  in  which  they  have  grown,  they  are  placed  in  fresh 
water  for  a  short  period  in  order  that  they  may  be  "fat- 
tened" or  "plumped"  by  the  absorption  of  water.  If  the 
water  in  which  they  are  placed  is  polluted  with  sewage,  the 
oyster  will  be  contaminated,  and  since  they  are  often  con- 
sumed raw,  opportunity  is  presented  for  the  transmission  of 
the  organism. 

The  house-fly. — Another  agency  in  the  distribution  of 
typhoid  fever  is  the  house-fly.  If  infectious  material  is 
deposited  where  flies  have  access  to  it,  they  may  carry  the 
organisms  to  the  food  with  which  they  come  in  contact. 
All  privy  vaults  should  be  so  constructed  that  flies  can  not 


BACTERIAL  CONTENT  165 

or  will  not  enter  them;  all  homes  and  all  places  in  which 
food  is  prepared  or  sold  should  be  effectively  screened. 

Diphtheria  and  scarlet  fever. — Diphtheria  and  scarlet 
fever  are  also  spread  by  means  of  milk.  The  opportunities 
for  the  contamination  of  foods  by  the  causal  organisms  of 
these  diseases  arfe  not  so  varied  as  in  the  case  of  typhoid 
fever.  It  is  probable  that  the  infection  is  largely  from 
mild  cases  that  are  not  recognized,  or  through  the  agency  of 
a  person  acting  in  the  dual  capacity  of  nurse  and  milker. 

The  influence  of  bacterial  content  on  healthfulness. — 
The  (luestion  concerning  the  effect  of  the  growth  of  sapro- 
phytic bacteria  in  food  on  its  healthfulness  is  an  important 
one,  since  a  large  proportion  of  the  food  materials  that 
reach  the  market  are  in  an  incipient  state  of  decomposition. 
Frequently  it  has  progressed  to  such  an  extent  as  to  be 
evident  to  the  senses.  The  value  of  such  food  is  lessened 
thereby.  The  question  as  to  its  absolute  rejection  as  human 
food  will  depend  on  whether  it  is  intrinsically  dangerous, 
rather  than  on  the  impression  it  may  make  on  those  whose 
economic  condition  is  such  that  they  can  afford  to  reject  it. 
There  is  little  reason  to  believe  that  decomposition  pro- 
cesses in  ordinary  foods  are  capable  of  producing  disease. 
This  is  especially  true  of  fruits,  and  possibly  less  true  of 
meats,  fish,  and  certain  vegetables. 

Many  common  foods  are  used  only  when  they  have  under- 
gone certain  types  of  decomposition.  The  same  type  of 
decomposition  in  another  food  would  cause  its  rejection 
for  esthetic  rather  than  for  hygienic  reasons.  In  a  general 
way,  it  may  be  said  that  the  control  of  foods  with  reference 
to  their  bacterial  content  is  an  economic  rather  than  a 
hygienic  matter,  and  there  would  seem  to  be  little  reason 
for  not  allowing  the  sale  of  foods  that  show  evidences  of 
decomposition  to  people  who  wish  to  purchase  them  at  a 
fair  price. 


166  AGRICULTURAL  BACTERIOLOGY 

It  is  believed  that  milk  in  which  a  considerable  amount 
of  bacterial  growth  has  occurred  is  less  healthful  that  milk 
of  lower  bacterial  content.  There  is  no  reason  to  believe 
that  the  organisms  of  the  Bad.  lactis  acidi  group  injure 
the  healthfulness  in  any  way,  no  matter  how  much  they 
may  have  grown  in  it.  There  are  many  other  groups  of 
bacteria  constantly  present  in  milk  for  which  such  an  asser- 
tion can  not  be  made  with  assurance.  Among  these  may 
be  classed  the  liquefying  bacteria  and  those  of  the  B.  coli- 
aerogenes  group. 

Infant  mortality. — It  is  thought  that  the  milk  supply  has 
much  to  do  with  the  high  death  rate  of  young  children. 
In  some  American  cities  more  than  40  per  cent,  of  the 
children  die  before  they  reach  one  year  of  age.  The 
greater  number  of  these  are  fed  on  some  substitute  for 
mothers'  milk,  cows'  milk  being  most  frequently  used.  It 
is  claimed  that  if  the  milk  were  of  better  quality,  if  it  con- 
tained less  bacteria,  and  had  undergone  less  decomposition, 
a  great  decrease  in  the  death  rate  of  artificially  fed  chil- 
dren would  be  noted.  It  is  certain  that  the  most  powerful 
factor  concerned  in  the  great  improvement  of  market  milk 
that  has  taken  place  in  recent  years  has  been  the  effort  to 
reduce  the  high  rate  of  infant  mortality. 

Poisonous  foods. — Substances  that  are  very  poisonous 
when  swallowed  are  formed  by  certain  bacteria,  the  most 
prominent  of  which  is  B.  hotulinus,  a  spore-forming  anaer- 
obic organism.  The  organism  received  its  name  from  the 
fact  that  it  was  first  found  in  sausage  (Latin,  hotulus,  sau- 
sage). For  some  time  it  was  thought  that  only  foods  of 
animal  origin  permitted  the  growth  of  this  organism.  More 
recently,  cases  of  botulinus  poisoning  have  been  traced  to 
various  vegetables.  In  almost  all  instances  the  trouble  has 
been  caused  by  the  use  of  canned  rather  than  fresh  mater- 
ials.    The  spores  of  the  organism  enable  it  to  resist  the 


POISONOUS  FOODS  167 

heat  treatment  that  the  foods  received,  and  its  anaerobic 
nature  enables  it  to  grow  in  the  cans,  which  are  practically 
devoid  of  air. 

The  toxic  substance  produced  by  this  organism  is  of  great 
potency.  As  small  a  quantity  as  0.01  cubic  centimeter  of 
a  glucose  broth  culture  can  produce  death  in  a  monkey  or 
rabbit  when  given  through  the  mouth.  The  extreme  tox- 
icity of  this  by-product  of  the  organism  may  make  a  food 
dangerous  before  any  signs  of  decomposition  are  apparent 
to  the  senses.  The  poisonous  substance  is  easily  destroyed 
by  heat.  If  a  canned  vegetable  or  meat  shows  the  slight- 
est sign  of  spoilage  it  should  not  be  used  for  food  until  it 
has  been  heated  to  the  boiling-point.  The  organism  itself 
is  unable  to  develop  in  the  animal  body.  The  injury  is 
due  to  a  preformed  product  which  is  ingested.  Thorough 
heating  of  foods  just  before  use  is  the  factor  of  safety 
against  organisms  harmful  either  in  themselves  or  because 
of  their  by-products. 


CHAPTER  XV 

THE  PRESERVATION  OF  FOODS 

It  is  impossible  to  handle  foods  in  such  a  manner  as  to 
prevent  microorganisms  from  coming  in  contact  with  them. 
With  greater  or  less  rapidity,  depending  on  whether  the  or- 
ganisms find  in  or  on  the  food  favorable  conditions  for 
growth,  decomposition  changes  will  ensue  and  the  food  be 
rendered  worthless.  In  a  previous  chapter  the  ways  in 
which  foods  become  seeded  with  microorganisms  were  stud- 
ied. The  more  cleanly  the  conditions  under  which  foods 
are  handled,  the  smaller  will  be  the  number  of  organisms 
brought  in  contact  with  them,  and  the  less  rapidly  will  the 
changes  take  place.  The  greater  the  number  of  organisms 
initially  present,  the  more  rapidly  the  decomposition 
changes  occur,  other  conditions  remaining  constant.  Hence, 
one  of  the  chief  ways  of  preserving  foods  is  to  prevent  their 
contamination  with  germ  life.  But  mere  prevention  of 
contamination  is  not  sufficient  and  must  be  supplemented 
by  other  means,  which  may  be  divided  roughly  into  three 
classes:  the  removal  of  microorganisms  from  foods;  their 
destruction;  and  the  establishment  of  conditions  that  will 
retard  or  prevent  their  growth.  These  methods  may  be 
used  singly  or  in  combination. 

The  microorganisms  that  adhere  to  the  surface  of  solid 
foods  may  often  be  removed  in  large  part  by  washing. 
Microorganisms  are  practically  always  contained  in  dirt 
and  other  matter  foreign  to  the  food.  Consequently,  the 
removal  of  this  dirt  will  tend  to  reduce  such  contamina- 
tion. Washing  or  wiping  of  fruits,  such  as  apples,  tends 
to  remove  the  molds  that  are  concerned  in  rotting  processes ; 

168 


PURIFICATION  OF  WATER  169 

and  the  washing  of  meats  and  of  many  other  foods  will  have 
some  infiiience  in  retarding  decomposition  changes. 

Purification  of  water. — Water  may  be  classed  as  a  food ; 
and,  wliile  it  is  not  subject  to  decomposition,  and  hence  one 
cannot  speak  of  preserving  it,  it  does  serve  to  distribute 
disease-producing  organisms.  The  measures  that  are  taken 
to  preserve  foods  often  serve  to  destroy  any  pathogenic  or- 
ganisms they  may  contain,  just  as  they  destroy  the  sapro- 
phytic organisms. 

Bacteria,  harmful  and  otherwise,  may  be  removed  from 
water  by  passing  it  through  filters  of  unglazed  porcelain. 
The  pores  of  these  filters  are  very  fine  and  tortuous,  so  that 
the  bacteria  are  held  back  even  though  the  pore  spaces  are 
of  greater  average  diameter  than  the  organisms.  If,  how- 
ever, the  filters  are  used  for  a  considerable  period  of  time 
without  cleaning,  some  forms  of  bacteria  will  multiply  in 
the  pores  and  the  filtrate  will  no  longer  be  sterile.  The 
filters  must  be  frequently  cleaned  and  sterilized,  if  they  are 
to  function  in  an  efficient  manner.  The  purification  of 
water  in  percolating  through  the  soil  is  also  due  to  the  same 
principle. 

Many  cities  purify  their  water  supplies  by  filtering  sur- 
face waters  through  filters  composed  of  layers  of  gravel 
and  sand,  arranged  so  that  the  finer  material  is  on  the 
surface.  The  upper  surface  of  the  filter  soon  becomes 
coated  with  a  gelatinous  layer  of  bacteria  and  sediment 
which  is  so  coherent  that  it  prevents  the  organisms  in  the 
water  from  passing  through  the  sand.  As  this  sediment 
layer  increases  in  thickness,  it  becomes  less  permeable, 
thus  reducing  the  amount  of  water  that  will  pass  the  filter. 
In  time  this  filtering  surface  must  be  removed.  For  the 
first  few  days  after  this  disturbance,  the  efficiency  of  the 
filtration  process  is  reduced,  until  the  gelatinous  layer  is 
reestablished.     By  means  of  this  process,  it  is  possible  to 


170  AGRICULTURAL  BACTERIOLOGY 

reduce  the  bacterial  content  of  surface  waters  from  95  to 
99  per  cent,  and  to  eliminate  practically  all  danger  from 
typhoid  and  other  water-borne  diseases. 

Another  method  of  purifying  water  supplies  consists  of 
producing  gelatinous  precipitates  by  the  addition  of  chem- 
ical agents  such  as  salts  of  iron  or  aluminum.  When  these 
are  added  to  water  containing  lime  in  solution,  insoluble 
compounds  of  a  jellylike  nature  are  formed.  All  fine  par- 
ticles, including  bacteria,  are  enmeshed  in  the  gelatinous 
material,  and  thus  can  be  removed  readily  by  sedimenta- 
tion or  filtration.  When  water  so  treated  is  passed  through 
coarse  filters,  these  gelatinous  precipitates  are  readily  re- 
moved, and  the  water  thereby  not  only  clarified,  but  its 
germ  content  materially  reduced. 

The  fine  turbidity  present  in  wines  is  removed  in  a  sim- 
ilar way.  When  small  quantities  .  of  gelatin  are  added, 
the  tannin  naturally  present  in  wines  causes  to  be  pro- 
duced an  insoluble  gelatinous  precipitate  that  is  readily  re- 
moved by  filtration. 

The  harmful  organisms  in  water  may  be  destroyed  by 
heating  it  to  the  boiling-point.  They  may  also  be  killed  by 
adding  to  the  water  a  minute  quantity  of  calcium  hypo- 
chlorite or  bleaching  powder,  which  has  a  powerful  ger- 
micidal action  in  the  absence  of  all  but  traces  of  organic 
matter.  The  odor  and  taste  of  chlorine  is  at  first  evident 
in  the  treated  water.  This  soon  disappears  and  the  hypo- 
chlorite is  changed  into  harmless  substances.  One  part 
of  the  reagent  to  one  million  parts  of  water  is  often  suffi- 
cient to  destroy  99  per  cent,  of  the  bacteria  therein.  The 
treatment  is  applicable  to  any  quantity  of  water.  Some 
large  cities  chlorinate  their  entire  supply.  The  water  sup- 
plies of  the  armies  in  the  recent  war  were  safeguarded  by 
adding  hypochlorite  to  the  water-tanks  whenever  they 
were  filled. 


DESICCATION  171 

Inhibition  of  microorganisms. — It  is  impossible  to  pro- 
duce and  j)repare  foods  without  contaminating  them  with 
microorganisms.  No  appreciable  decomposition  can  take 
place  without  the  actual  growth  of  the  organisms.  Any 
treatment  that  will  inhibit  or  prevent  the  growth  of  bac- 
teria and  allied  organisms  will  favor  the  preservation  of 
food  supplies.  Many  chemical  and  physical  agents  influ- 
ence the  proliferation  of  microorganisms. 

Desiccation. — Nature's  method  of  protecting  organic 
matter  from  spoilage  is  by  the  removal  of  water.  It  is  by 
far  the  most  important  way  of  preserving  foods  and  fodders. 
The  great  staple  foods,  grains,  flours,  meals,  hays,  and 
other  roughages,  are  thus  preserved.  Fruits  as  raisins,  cur- 
rants, and  prunes  are  protected  by  drj^ing  in  the  sun.  The 
artificial  dehydration  of  vegetables  has  made  great  pro- 
gress and  is  destined  to  become  more  important  as  time 
passes.  The  process  obviates  the  transportation  of  large 
quantities  of  water  and  the  use  of  expensive  containers. 
When  appropriate  means  of  drying  are  used,  the  natural 
flavor  and  texture  of  the  original  materials  are  restored  by 
allowing  them  to  take  up  water. 

The  dry  foods  absorb  water  if  kept  in  a  damp  atmo- 
sphere. The  molds,  due  to  their  ability  to  secure  water 
where  other  organisms  can  not,  are  the  first  to  appear  on 
the  moist  food.  The  molding  of  hay  and  grain  are  impor- 
tant examples  of  the  ability  of  molds  to  grow  in  the  pres- 
ence of  small  quantities  of  water.  Meats,  fish,  eggs,  and 
milk  are  preserved  by  the  removal  of  water.  Edible  oils, 
such  as  olive  and  cottonseed,  owe  their  keeping  qualities 
to  their  freedom  from  water. 

Preservation  by  concentration. — In  an  earlier  part  of 
this  book  the  relation  of  the  cell  to  the  density  of  the 
liquid  surrounding  it  was  presented.  It  was  shown  that 
the  ease  with  which  the  cell  is  plazmolyzed  varies  widely  with 


172  AGRICULTURAL  BACTERIOLOGY 

the  different  groups  of  microorganisms.  As  a  group,  the 
bacteria  are  the  least  resistant  to  the  action  of  solutions  of 
high  osmotic  pressure;  the  molds  are  the  most  resistant. 
This  differentiation  in  the  ability  of  organisms  to  grow  in 
concentrated  solutions  is  of  great  importance  in  food  preser- 
vation. Concentration  alone  can  not  usvially  be  relied 
upon  to  protect  food  materials,  but  must  be  supplemented 
by  some  other  agent  or  process.  Frequently  heat  is  ap- 
plied in  concentrating  the  material,  as  in  preparing  syrups 
from  the  sap  of  the  cane,  the  beet,  or  the  maple ;  or  heat 
is  applied  in  the  preparation  of  the  food  after  the  concen- 
tration has  been  raised  by  the  addition  of  sugar  or  salt. 
The  yeasts  and  molds  that  are  most  likely  to  grow  in  such 
materials  are  destroyed  by  the  heat;  and,  unless  recontam- 
ination  occurs,  the  food  should  keep.  The  exclusion  of  air, 
thus  preventing  mold  growth,  is  another  supplementary 
factor. 

Syrups  owe  their  keeping  qualities  to  their  concentration. 
If  these  sugary  liquids  are  insufficiently  concentrated,  they 
undergo  most  commonly  an  acid  fermentation,  caused  by 
bacteria.  Condensed  milk  is  prepared  by  the  concentration 
of  fresh  milk  and  by  the  addition  of  cane  sugar.  Jellies 
and  jams  are  protected  from  bacteria  by  their  concentra- 
tion. The  heating  they  receive  in  preparation  frees  them 
from  yeasts,  and  mold  growth  is  prevented  by  covering  the 
surface  with  a  layer  of  paraffin.  The  addition  of  salt 
to  meats  and  fish,  coupled  with  partial  drying,  is  a  com- 
mon practice.  The  same  materials  may  also  be  preserved 
by  placing  them  in  a  saturated  solution  of  salt. 

Preservatives. — Many  chemical  substances  exert  an  in- 
jurious effect  on  microorganisms,  inhibiting  their  growth 
when  present  in  such  minute  quantities  that  their  effect 
can  not  be  ascribed  to  physical  action.     They  act  chemi- 


DESICCATION  173 

cally,  and  are  usually  called  preservatives.  Among  those 
most  commonly  employed  have  been  boric  acid  and  bor- 
ates, benzoic  acid  and  its  salts,  salicylic  acid,  and  formalin. 
Boric  acid  is  used  in  butter,  especially  in  that  made  in  New 
Zealand  and  Australia  to  be  shipped  to  the  English  mar- 
kets. Benzoic  acid  is  used  in  catsups  and  ciders,  while 
salicylic  acid  is  contained  in  the  canning  powders  that  have 
been  widely  sold  in  the  past.  Formalin  has  often  been 
used  in  milk.  One  part  of  formalin  to  ten  thousand  parts 
of  milk  will  have  a  marked  inhibiting  effect  on  bacterial 
growth.  The  use  of  such  chemicals  in  foods  is  prohibited 
by  law  in  most  States,  and  by  the  national  government  in 
its  control  of  the  interstate  commerce  in  foods.  The  use 
of  benzoates  is  allowed  in  certain  foods,  but  the  amount 
used  must  be  stated  on  the  label. 

As  to  the  effect  of  such  preservatives  on  health,  different 
views  are  held  by  various  authorities.  The  prohibition  of 
their  use  is  a  wise  one,  since  the  foods  in  which  they  would 
be  used  can  be  preserved  by  other  means  concerning  which 
there  is  no  (juestion  as  to  their  effect  on  the  health  of  con- 
sumers. 

Certain  chemicals  sometimes  added  to  foods  unite  with 
definite  decomposition  products,  thus  masking  the  effect  of 
the  changes  produced.  If  sodium  bicarbonate  is  added  to 
milk,  it  combines  with  the  lactic  acid,  and  thus  reduces  the 
acidity  of  tlie  product.  Sulphites  are  used  with  meats, 
particularly  chopped  meats,  to  impart  a  bright  red  color 
to  the  same  and  to  neutralize  the  odors  produced  in  putre- 
factive changes.  Potassium  nitrate  is  used  in  corned  beef. 
Some  of  the  nitrate  is  reduced  to  nitrite,  which  is  an  active 
agent.  It  also  imparts  a  bright  red  color  to  the  meat.  The 
use  of  this  latter  substance  is  not  regarded  as  dangerous. 
Generally  speaking,  such  chemicals  can  be  used  in  suffi- 


174  AGRICULTURAL  BACTERIOLOGY 

cient  amounts  to  accomplish  the  desired  result  without  being 
apparent  to  the  taste.  If  their  use  were  sanctioned  by 
law,  materials  unfit  for  food  would  be  sold. 

Some  of  the  condiments,  such  as  cloves,  cinnamon,  and 
mustard,  contain  essential  oils  that  have  a  preservative  ac- 
tion that  is  more  marked  on  molds  than  on  bacteria.  They 
are  used  especially  in  pickles,  catsups,  mincemeat,  and 
fruit-cake.  No  regulations  concerning  their  use  are  needed, 
for  the  reason  that  the  amount  that  can  be  added  to  a  food 
is  limited  because  of  their  influence  on  flavors. 

In  the  smoking  of  meats,  chemical  compounds  of  the 
creosote  type  are  produced  by  the  slow  or  imperfect  com- 
bustion of  wood,  and  are  deposited  on  the  surface  of  the 
meats.  Certain  woods,  such  as  beechwood,  yield  a  special 
flavor  that  is  much  prized.  Of  later  years  the  so-called 
liquid  smoke,  which  is  a  by-product  of  wood  distillation,  is 
often  used  as  a  surface  application.  Its  value  as  a  pre- 
servative depends  on  the  disinfecting  actfon  of  the  creo- 
sote. 

Organic  acids. — Organic  acids  are  widely  used  in  the 
preservation  of  foods.  The  acids  may  be  formed  in  the 
foods  by  decomposition  processes,  or  they  may  be  added, 
as  in  the  case  of  the  addition  of  vinegar  to  pickles.  Sauer- 
kraut is  prepared  by  cutting  cabbage  and  packing  it  tightly 
in  vessels  with  2  per  cent,  of  common  salt.  The  pressure 
and  the  action  of  the  salt  extract  the  juices  from  the  plant 
tissue.  This  liquid,  which  contains  sugar,  protein  material, 
and  various  salts,  makes  an  excellent  medium  for  the 
growth  of  lactic-acid-forming  bacteria.  The  amount  of 
acidity  thus  produced  is  sufficient  to  inhibit  entirely  all  de- 
velopment of  putrefactive  bacteria.  As  long  as  the  acid 
reaction  is  maintained,  the  kraut  remains  edible.  The  acid 
may,  however,  be  destroyed  by  the  growth  of  molds  and 
yeasts  on  the  surface  of  the  liquid,  but  if  the  sauerkraut  is 


PRESERVATIVES  175 

placed  in  kegs  and  thus  kept  from  the  air,  no  mold  growth 
can  take  place.  The  action  of  acid-forming  bacteria  is  also 
important  in  the  preservation  of  certain  pickles,  especially 
cucumber  pickles  made  in  brine. 

Silage. — The  preservation  of  green  fodder,  especially 
corn,  has  become  of  great  economic  importance.  It  is 
customary  to  cut  the  material  to  be  ensiled  into  short  pieces, 
so  that  it  may  be  closel}-  packed.  This  process  permits 
the  sap  to  exude,  and  gives  the  bacteria  that  were  on  the 
surface  of  the  tissue  access  to  it.  Bacterial  growth  is 
rapid;  lactic  and  acetic  acids  soon  accumulate  to  such  an 
extent  as  to  exclude  the  growth  of  putrefactive  forms.  The 
fresh  vegetable  tissue  carries  large  numbers  of  acid-form- 
ing bacteria  on  its  surface,  so  that  no  inoculation  is  nec- 
essary. 

The  oxygen  of  the  air  between  the  pieces  of  ensiled  ma- 
terial is  soon  exhausted  by  the  respiratory  processes  of  the 
cells  of  the  plant  tissue.  The  result  is  that  the  air  consists 
of  carbon-dioxide  and  nitrogen.  No  molds  can  grow  under 
these  conditions.  If  the  wall  of  the  silo  is  so  constructed 
that  no  air  can  pass  through  it,  and  if  the  silage  is  closely 
packed,  so  that  air  can  not  penetrate  deeply  into  it  from 
the  surface,  the  acid  mass  will  keep  for  an  indefinite  time. 

In  those  areas  in  which  molds  grow,  as  near  the  surface, 
the  acid  will  be  destroyed  and  conditions  thus  established 
that  will  permit  the  growth  of  putrefactive  bacteria.  The 
silage  in  these  places  will  be  dark  in  color  and  will  have  an 
offensive  odor,  and  the  tissues  will  have  disintegrated, 
while  that  in  which  the  growth  of  molds  and  putrefactive 
bacteria  has  been  prevented  will  show  none  of  these 
changes. 

Preservation  by  low  temperature. —  The  use  of  low  tem- 
peratures to  restrain  or  prevent  the  growth  of  microor- 
ganisms is  of  the  greatest  importance.     The  methods  in- 


176  AGRICULTURAL  BACTERIOLOGY 

volved  in  artificial  refrigeration  and  their  application  to 
the  cold-storage  industry  are  largely  the  outcome  of  the 
relation  of  cold  to  the  preservation  of  food  supplies. 

The  temperature  zone  within  which  bacterial  growth  can 
take  place  extends  from  a  few  degrees  below  the  freezing 
point  of  water  to  about  158  °  F.  It  is  true  that  no  one 
organism  possesses  the  ability  of  growing  throughout  this 
entire  range  of  temperature.  Most  kinds  are  able  to  de- 
velop from  temperatures  in  the  neighborhood  of  50  °  F. 
to  somewhat  above  blood  heat.  Also  there  are  groups  cap- 
able of  multiplying  at  or  near  the  freezing-point,  and 
others  at  temperatures  of  120-140  °  F.  Those  types  habi- 
tuated to  low  temperatures  are  of  much  practical  signifi- 
cance in  the  storage  of  foods. 

The  greatest  importance  of  low  temperatures  in  the 
preservation  of  foods  is  not  found  in  the  extreme  temper- 
atures that  are  employed  in  cold-storage  warehouses,  but 
in  the  range  that  occurs  in  daily  life  under  the  conditions 
obtaining  in  the  ordinary  household.  The  great  majority 
of  bacteria  grow  most  rapidly  from  60  °  to  100  °  F.  If  the 
temperature  is  reduced  to  50°,  the  rate  of  bacterial  multi- 
plication is  much  retarded,  as  is  to  be  noted  from  the  fol- 
lowing table  in  which  is  given  the  time  required  for  the 
division  of  a  single  bacterial  cell  into  two  completely  grown 
daughter  cells  at  different  temperatures. 

The  generation  time  of  B.  coli 
45°  C.  (113°  F.)  20      minutes 


40°  C. 

(104°  F.) 

17.2 

minutes 

35°  C. 

(   95°  F.) 

22 

minutes 

30°  C. 

(   86°  F.) 

29 

minutes 

25°  C. 

(   77°  F.) 

40 

minutes 

20°  C. 

(   68°  F.) 

95 

minutes 

16°  C. 

(   60°  F.) 

120 

minutes 

10°  C. 

(   50°   F.) 

14 

hours,  25  min. 

As  ordinary  refrigerators  maintain  a  temperature  vary- 


LOW  TEMPERATURES  177 

ing  from  45°  to  50°  F.,  it  is  evident  that  bacterial  growth 
is  greatly  retarded  by  maintenance  of  food  material  under 
readily  available  low-temperature  conditions. 

The  zone  of  bacterial  existence  is  far  wider  than  the 
zone  of  growth.  This  fact  is  of  importance  in  the  storage 
of  foods,  for  wh^n  they  are  removed  from  storage,  the 
microorganisms  that  were  present  when  the  foods  went  into 
storage  begin  to  grow,  and  the  decomposition  changes  rap- 
idly occur.  Indeed,  with  some  foods,  especially  meats, 
these  changes  develop  after  freezing  with  even  increased 
rapidity,  owing  to  the  fact  that  the  muscle  fibers  are  forced 
apart  by  the  freezing  process,  allowing  the  cell  juices  to 
exude  from  the  cells  themselves.  This  permits  the  bacteria 
to  act  more  readily  on  the  meat  than  when  confined  ex- 
clusively to  the  surface.  Even  after  storage  at  extremely 
low  temperatures,  below  0°  F.,  foods  spoil  rapidly;  for 
while  alternate  freezing  and  thawing  are  very  injurious  to 
bacterial  life,  microorganisms  are  able  to  withstand  expos- 
ure to  low  temperatures  for  prolonged  periods  of  time. 

In  the  storage  of  foods  at  low  temperatures,  the  effect 
of  freezing  on  the  physical  properties  of  food  must  be 
considered.  For  example,  eggs,  fruits,  and  vegetables  can 
not  be  stored  without  injury  at  temperatures  at  which 
freezing  will  occur.  If  milk  is  frozen  and  allowed  to  re- 
main in  this  condition  for  any  considerable  period,  the  fat 
is  altered  physically,  so  that  on  thawing  it  does  not  mix 
thoroughly  with  the  serum.  Longer  exposure  causes  the 
casein  to  separate. 

In  the  case  of  foods  that  can  be  stored  with  impunity  at 
temperatures  below  freezing,  the  period  of  storage  may  be 
greatly  extended;  but  with  such  foods  as  milk  and  eggs, 
where  storage  must  be  above  freezing,  the  holding  period 
is  limited  because  of  the  fact  that  bacterial  development 
can   occur   at   temperatures   slightly   above   freezing.     In 


178  AGRICULTURAL  BACTERIOLOGY 

milk  the  development  of  the  acid-forming  bacteria  is 
stopped  at  these  temperatures;  consequently  the  milk  may 
not  undergo  the  customary  souring  change,  but  other 
bacterial  types  that  act  on  the  casein  can  grow  slowly  at 
these  low  temperatures,  rendering  the  milk  unfit  for  use 
within  a  few  weeks.  It  is  believed  that  many  of  the  cases 
of  poisoning  due  to  ice  cream  have  been  caused  as  a  result 
of  the  storage  of  cream,  a  practice  that  has  now  been  largely 
abandoned. 

Even  in  the  case  of  foods  that  are  not  contaminated, 
by  microorganisms,  changes  may  go  on  that  limit  the  time 
that  the  food  can  be  held  in  storage.  These  changes  are 
due  to  the  enzymes  that  are  normally  present  in  many 
uncooked  foods,  and  are  usually  termed  autolytic  changes. 
The  ripening  of  meats  is  an  example.  In  the  case  of  eggs 
the  white  becomes  less  viscous,  and  loses  to  some  extent  its 
beating  properties.  Water  also  passes  from  the  white  into 
the  yolk;  the  membrane  surrounding  the  yolk  weakens,  so 
that  when  the  egg  is  broken,  it  is  difficult  to  avoid  mixing 
the  yolk  with  the  white. 

Preservation  of  eggs. — In  preserving  eggs  it  is  necessary 
to  prevent  the  invasion  by  bacteria  and  to  limit  the  loss  of 
water  from  the  eggs.  Eggs  are  practically  sterile  when 
laid,  but,  owing  to  the  porous  nature  of  the  shell,  bacteria 
are  able  to  penetrate  it  readily  if  the  surface  of  the  egg  is 
moist.  These  organisms  penetrate  the  shell  in  the  same 
manner  as  they  do  the  wall  of  a  porcelain  filter,  i.  e.,  by 
growing  through  it.  If  the  eggs  are  left  in  a  dirty  nest, 
or  placed  in  a  damp  cellar,  the  adhering  moisture  may  be 
sufficient  to  enable  the  bacteria  on  the  shell  to  multiply  and 
so  penetrate  the  shell.  In  cold-storage  rooms  it  is  essen- 
tial that  the  temperature  be  kept  constant,  so  that  moisture 
will  not  condense  on  the  surface  of  the  eggs. 

For  home  use,  eggs  may  be  preserved  by  placing  them 


HEAT  179 

in  some  liquid  in  which  bacterial  growth  can  not  take  place, 
but  the  liquid  must  be  of  such  a  nature  that  it  will  not  be 
absorbed  by  the  eggs.  For  this  purpose  sodium  silicate, 
or  water-glasSy  is  most  frequently  employed.  The  colloidal 
nature  of  this  silicate  prevents  its  passage  into  the  egg,  and 
the  alkalinity  of  the  solution  stops  all  bacterial  growth. 
No  desiccation  can,  of  course,  take  place.  If  the  eggs  have 
been  invaded  by  bacteria  before  placing  them  in  the  water- 
glass,  the  growth  of  the  bacteria  will  not  be  inhibited.  In 
such  cases,  gaseous  by-products  may  be  formed  in  the  q^^ 
to  sueli  an  extent  that  rupture  of  the  shell  occurs,  in  which 
case  the  ill-smelling  decomposition  products  will  be  ab- 
sorbed by  the  remaining  eggs  to  such  a  degree  as  to  injure 
their  commercial  value.  The  best  practice  is  to  place  the 
eggs  in  watcr-frlass  the  same  day  they  are  laid. 

Preservation  by  heat. — Virtually  the  only  way  by  which 
the  microorganisms  present  in  any  food  can  be  completely 
destroyed  is  by  the  application  of  heat.  The  vegetative 
cells  of  bacteria,  yeasts,  and  molds  are  easily  destroyed 
when  subjected  to  temperatures  approximating  140°- 
150°  F.  The  spore  stages  of  all  types  are  more  resistant, 
but  particularly  so  with  the  bacteria  that  require  a  tem- 
perature exceeding  that  of  the  boiling-point  before  they 
can  be  completely  destroyed.  It  is  therefore  easy  to  free 
any  food  substance  from  all  organisms  except  the  spores 
of  bacteria. 

In  practice  two  processes  are  used :  first,  the  application 
of  a  temperature  slightly  exceeding  the  scalding-point  of 
water,  from  140°  to  165°  F.  This  process,  known  as  pas- 
teimzntion,  from  the  fact  that  it  was  first  employed  by 
Louis  Pasteur  in  the  treatment  of  wines  to  prevent  ab- 
normal changes,  does  not  destroy  all  microorganisms,  but 
only  those  in  the  vegetative  or  growing  stage.  The  more 
effective  process,  known  as  sterilization^  utilizes  tempera- 


180  AGRICULTURAL  BACTERIOLOGY 

tures  equaling  or  exceeding  the  boiling-point.  The  former 
method  is  employed  when  it  is  not  desired  to  keep  the  ma- 
terial for  long  periods,  as  in  the  commercial  handling  of 
milk.  It  is  also  used  when  the  presence  of  bacterial  spores 
is  of  no  importance,  because  of  the  fact  that  their  germi- 
nation is  prevented  by  the  reaction  of  the  material.  The 
higher  temperature  is  employed  in  the  preparation  of 
canned  foods  where  complete  destruction  of  bacterial  life 
is  necessary  to  preserve  such  material  for  relatively  long 
periods  of  time. 

Pasteurization  of  milk. — The  organisms  concerned  in  the 
spoiling  of  milk  are  non-spore-forming  bacteria,  and  are 
easily  destroyed.  Milk  may  also  contain  pathogenic  or- 
ganisms which  it  is  necessary  to  destroy.  Fortunately, 
those  disease  germs  that  are  likely  to  be  spread  through  the 
agency  of  milk  are  non-spore-forming,  so  that  protection 
of  milk  supplies  may  be  secured  through  pasteurization. 

In  the  treatment  of  any  food  with  heat,  the  physical 
effect  on  the  material  must  be  considered.  In  many  cases 
the  chemical  and  physical  changes  are  such  as  to  injure 
the  commercial  value  of  the  food.  If  milk  is  heated  above 
145°  F.  for  any  length  of  time,  the  process  of  creaming 
is  much  retarded.  The  fat  globules  in  milk  are  not  uni- 
formly distributed  throughout  the  entire  milk,  but  are 
grouped  in  masses  that  present  a  relatively  smaller  surface 
in  proportion  to  their  volume  than  do  the  separate  globules. 
The  viscosity  of  the  serum  is  such  that  it  offers  a  certain 
amount  of  resistance  to  the  rising  of  the  fat.  The  larger 
the  mass  of  fat  the  more  readily  does  it  rise  to  the  surface. 

In  the  commercial  handling  of  milk  in  bottles,  it  is  de- 
sirable that  the  creaming  take  place  rapidly,  since  an  in- 
distinct or  thin  cream  line  is  considered  by  the  consumer  as 
indicating  a  milk  low  in  fat  content.  The  cooked  taste 
that  is  imparted  to  milk  by  too  high  a  degree  of  heat  is  ob- 


HEAT  181 

jectionable  to  many  consumers.  It  has  often  been  stated 
that  heated  milk  is  less  digestible  and  likely  to  cause  nu- 
tritional troubles  in  children. 

Milk  contains  growth-stimulating  substances  of  an  un- 
known nature.  These  bodies  are  known  as  vitamines.  The 
heating  of  milk  partially  destroys  these  important  sub- 
stances, and  for  that  reason  becomes  an  objectionable  proc- 
ess. The  advantages  of  pasteurization  greatly  outweigh 
the  disadvantages.  If  it  seems  desirable,  the  loss  of  vita- 
mines  in  milk,  due  to  the  heating  thereof,  can  be  compen- 
sated for  by  the  feeding  of  fruit  juice,  especially  that  of 
the  orange.  Cases  of  malnutrition  and  abnormal  develop- 
ment of  the  bones,  rickets,  have  likewise  been  ascribed  to 
heated  or  pasteurized  milk.  But  there  is  no  reason  to  be- 
lieve that  milk  as  now  treated  is  more  likely  to  be  the 
cause  of  such  troubles  than  is  raw  milk.  In  fact,  milk 
heated  to  the  boiling-point  is  successfully  used  with  chil- 
dren. 

In  the  treatment  of  any  food  the  degree  of  heat  necessary 
to  destroy  the  organisms  is  dependent  on  the  length  of  time 
the  material  is  exposed  to  its  action.  Low  temperatures 
for  long  periods  of  time  may  be  as  effective  as  higher  tem- 
peratures for  shorter  exposures.  In  the  pasteurization  of 
milk,  the  exposure  may  be  at  145°  F.  for  from  twenty  to 
thirty  minutes  or  160°  F.  for  dne  minute.  Either  of  these 
methods  will  insure  the  freedom  of  the  milk  from  patho- 
genic bacteria,  and  will  destroy  such  a  proportion  of  the 
acid-forming  bacteria  as  to  improve  the  keeping  qualities 
of  milk.  In  actual  practice  no  method  has  been  devised 
by  which  milk  can  be  heated  momentarily  with  perfect  suc- 
cess. In  machines  designed  for  this  so-called  fla^h  method 
of  heating,  the  milk  is  allowed  to  flow  through  the  heating- 
chamber  in  a  continuous  stream.  In  such  a  device  the 
rate  of  flow  is  not  uniform  in  all  parts  of  the  machine. 


182 


AGRICULTURAL  BACTERIOLOGY 


The  milk  in  contact  with  the  walls  flows  less  rapidly  than 
that  iii  the  middle  of  the  machine;  consequently,  while 
some  of  it  may  be  heated  sufficiently  long  to  permit  of  the 
thorough  destruction  of  all  disease-producing  bacteria,  if 

they  are  present,  other 
portions  may  be  insuffi- 
ciently heated.  When 
the  possibility  exists 
that  such  orfianisms  as 
the  typhoid  and  tubercle 
bacteria  may  be  present, 
it  is  apparent  that  no 
method  can  be  regarded 
as  entirely  satisfactory 
that  will  not  insure  the 
destruction  of  these 
types. 

While  this  flash 
method  of  pasteuriza- 
tion was  earlier  adopted 
by  many  milk  dealers 
for  the  treatment  of 
milk  supplies,  it  has  not 
been  with  the  full  ap- 
proval of  health  authori- 
ties, and  gradually  it  has  been  displaced  by  the  more  effi- 
cient holding  method.  The  fundamental  principle  of  the 
holding  process  is  that  a  given  quantity  of  milk  can  be  held 
at  any  desired  temperature  for  any  given  length  of  time. 
This  makes  it  possible  to  treat  the  milk  in  such  a  way  as 
to  insure  perfect  safety,  through  the  complete  destruction 
of  disease-producing  organisms.    . 

In  the  methods  described  the  destruction  of  all  bacteria 
is  not  attained.     To  prevent  the  rapid  development,  it  is 


A  Home;Made  Pasteurizer 

milk    is    known    to    be    safe,    it 

pasteurized     in     the     home.     A 

tumbler  is  a  convenient  cover  for  the  milk 

bottle    during    pasteurization    and    storage. 

A  floating  dairy  thermometer  is  desirable 


Fig 

Unless    the 
should    be 


HEAT  183 

essential  that  the  pasteurized  milk  be  cooled  quickly  and 
stored  at  a  low  temperature.  As  milk  is  commercially  han- 
dled, not  all  of  the  acid-forming  bacteria  are  killed ;  hence, 
pasteurized  milk  sours  as  does  raw  milk,  but  the  process 
is  materially  delayed.  If  heated  at  the  higher  pasteurizing 
limits,  all  but  the  spore-forming  bacteria  will  be  destroyed. 
Such  milk  will  not  sour,  but  decomposition  changes  will 
occur:  in  which  the  casein  and  albumen  will  undergo  a 
change. 

Pasteurization  of  other  liquid  products  is  frequently  em- 
ployed. Beer  is  heated  to  low  temperatures  after  it  is 
placed  in  bottles,  to  prevent  the  appearance  of  fermenta- 
tions that  might  impart  an  undesirable  taste  and  appear- 
ance. The  presence  of  alcohol  and  some  of  the  extractives 
from  the  hops  tends  to  prevent  the  growth  of  the  bacteria 
that  have  not  been  killed  by  the  heating.  Wines  arc  also 
heated  in  a  similar  way  to  overcome  the  turbidity  that 
sometimes  results  from  bacterial  changes. 

Such  acid  products  as  tomatoes,  rhubarb,  and  grape  juice 
can  be  preserved  by  a  short  exposure  at  the  boiling-point. 
This  insures  the  destruction  of  all  but  the  spores  of  bac- 
teria, the  development  of  which  is  prevented  by  the  acid 
reaction.  To  obviate  subsequent  infection,  it  is  advisable 
to  treat  such  material  after  it  has  been  placed  in  con- 
tainers. Such  a  method  has  recently  been  introduced  with 
milk,  but  the-  attendant  expense  is  such  that  it  has  not  been 
generally  adopted  by  milk  dealers,  even  though  it  would 
insure  complete  immunity  from  milk-borne  disease. 

Preservation  by  sterilization. — The  indefinite  preserva- 
tion of  foods  in  closed  containers  has  been  rendered  possi- 
ble through  the  application  of  the  process  of  sterilization. 
On  this  principle  rests  the  great  development  of  the  can- 
ning industry,  which  has  assumed  such  tremendous  propor- 
tions of  late  years.     While  it  is  impossible  to  raise  the  tem- 


184  AGRICULTURAL  BACTERIOLOGY 

perature  of  boiling  water  above  212°  F.,  the  temperature 
of  steam  when  confined  increases  rapidly  above  that  point. 
Under  a  steam  pressure  of  fifteen  pounds  to  the  square 
inch,  a  temperature  of  248°  F.  is  attained,  which  is  suffi- 
cient to  destroy  all  forms  of  bacterial  life,  even  the  most 
resistant  spores. 

In  the  treatment  of  many  foods,  the  heating  process  can 
not  be  continued  for  too  long  a  period  without  injury  to 
the  physical  properties  of  the  product,  as,  for  instance, 
with  milk  heating  at  excessive  temperatures  causes  the 
casein  to  curdle.  In  the  treatment  of  peas,  if  heated  at  too 
high  a  temperature  or  for  a  prolonged  period,  some  of  the 
peas  crack  open,  allowing  the  contents  to  escape.  This 
results  in  a  turbid  liquid  which  is  unattractive  and  gives 
the  impression  of  an  abnormal  fermentation.  To  prevent 
this  the  cans  should  be  exposed  for  a  longer  time  at  a  lower 
temperature.  In  the  earlier  days  of  the  canning  industry 
much  loss  was  occasioned  from  the  development  of  abnor- 
mal fermentations,  due  to  the  growth  of  gas-producing  bac- 
teria, the  spores  of  which  were  not  destroyed  by  insufficient 
sterilization.  Even  under  the  anaerobic  conditions  that 
prevailed  in  the  closed  container,  luxuriant  germ  growth 
could  occur. 

With  milk,  peas,  and  vegetables,  the  reaction  of  the  liquid 
is  sufficiently  neutral  to  permit  of  the  ready  germination 
of  any  spores  that  may  have  escaped  destruction  in  the 
heating  process.  Since  gas  is  generally  produced  as  a  re- 
sult of  such  fermentation,  spoiled  food  products  preserved 
in  tin  containers  can  usually  be  detected  by  the  bulging 
of  the  ends  of  the  can.  This  pressure  may  develop  to  the 
point  where  the  cans  actually  explode.  In  the  treatment 
of  meat  products,  there  is  no  practical  danger  of  over- 
heating, so  the  losses  that  occur  are  relatively  small. 

In  household  preservation  of  vegetables,  sterility  can  be 


HEAT  185 

secured  by  heating  the  product  to  the  boilingr-point  on  three 
successive  days,  as  described  on  page  36.  Small  steam- 
pressure  cookers  have  also  been  recently  introduced  for 
household  use.  In  the  canning  of  fruits  in  the  home,  the 
sugar  that  is  added  for  flavor  aids  in  the  preserving  process, 
through  the  fact  that  it  increases  the  concentration  of  the 
liquid  and  also  raises  the  boiling-point  of  the  solution  so 
that  the  spores  are  subjected  to  a  temperature  above 
212°  F. 

It  has  been  shown  by  recent  investigation  that  much-  of 
the  canned  material  is  not  sterile.  It  is  not  essential  that 
any  material  be  free  from  all  living  microorganisms  or 
their  spores  in  order  to  be  protected  from  decomposition. 
If  the  organisms  present  are  unable  to  grow  under  the  con- 
ditions that  obtain  in  the  material,  their  presence  is  of  no 
importance.  The  spores  of  many  aerobic  bacteria  are 
among  the  most  resistant,  and  are  most  likely  to  persist 
in  foods  after  processing.  In  the  sealed  can  that  has  been 
largely  freed  from  air  before  being  sealed^  the  aerobic 
spores  can  not  germinate.  The  spores  of  anaerobic  bac- 
teria in  the  food  are  far  more  likely  to  cause  trouble  in 
canned  goods  than  those  of  aerobic  forms.  The  develop- 
ment of  the  spores  of  anaerobic  forms  may  be  prevented  by 
concentration,  acids,  and  preservatives. 


CHAPTER  XVI 

THE  FERMENTATIONS  OCCURRING  IN  FOOD 
PRODUCTS 

In  the  preparation  and  handling  of  foods,  they  inevitably 
become  seeded  with  a  great  variety  of  organisms.  This 
contamination  is  a  more  or  less  constant  factor,  in  that 
representatives  of  the  three  great  groups  of  microorgan- 
isms, the  bacteria,  yeasts,  and  molds,  are  always  introduced. 
The  relation  between  the  groups  will  vary,  depending  on 
the  nature  of  the  food  material.  Whether  one  group  or 
another  is  to  be  most  active  in  the  decomposition  changes 
will  depend  on  the  composition  and  concentration  of  the 
material.  Such  foods  as  meats,  which  are  high  in  protein 
and  low  in  carbohydrates,  undergo  putrefactive  changes, 
due  to  bacteria  that  act  primarily  on  the  protein.  If  the 
material  contains  a  large  amount  of  sugar  in  proportion 
to  the  protein,  and  the  reaction  is  not  acid,  the  type  of 
fermentation  will  be  similar  to  that  noted  in  milk  in  which 
the  sugar  is  fermented  with  the  production  of  acid,  and 
the  protein  is  not  attacked  to  any  degree.  If  the  material 
contains  sugar  and  has  an  acid  reaction,  a  condition  found 
in  many  fruit  juices,  yeasts  are  likely  to  be  the  dominant 
type  of  organism  concerned  in  its  decomposition.  Alcohol 
and  carbon-dioxide  are  the  chief  products  of  yeast  action. 

The  acid  fermentation  of  milk. — The  souring  of  milk 
is  so  common  that  it  is  looked  upon  as  a  normal  change ;  in 
fact,  its  absence  is  more  likely  to  be  regarded  as  an  abnor- 
mal condition  than  is  its  occurrence.  If  milk  could  be 
secured    without    microorganisms,    it    would    remain    un- 

186 


ACID  FERMENTATION  OF  MILK  187 

changed  for  many  days;  but,  in  the  normal  course  of 
events,  it  invariably  becomes  seeded  with  a  variety  of 
organisms,  which  in  a  short  course  of  time  are  able  to  de- 
velop and  produce  the  characteristic  fermentative  by-prod- 
ucts that  bring  about  the  usual  changes  noted.  These 
changes  are  not  produced  by  a  specific  organism,  but  by  a 
group  of  widely  dissimilar  species  as  far  as  form  is  con- 
cerned, which,  however,  are  able  to  produce  varying 
amounts  of  acids,  particularly  lactic  acid.  While  this  fer- 
mentation product  is  produced  in  such  quantities  as  to 
characterize  the  change  involved,  yet  olher  by-products  are 
likewise  formed,  as  other  acids,  gases,  and  various  sub- 
stances. Some  of  these  flavor-forming  products  may  be  of 
value,  as  in  the  case  of  those  producing  agreeable  flavors 
in  butter. 

The  curdling  of  milk. — The  casein  of  milk  is  not  in 
actual  solution,  but  exists  in  a  colloidal  condition  in  combi- 
nation with  calcium.  As  the  bacteria  multiply,  a  portion 
of  the  sugar  that  they  use  is  changed  to  acid,  which  com- 
bines with  the  calcium,  leaving  the  casein  free,  in  which 
condition  it  is  precipitated  in  the  form  of  curd. 

The  bacteria  that  are  primarily  concerned  in  the  acid 
fermentation  of  milk  may  be  divided  into  two  groups.  The 
name  Bad.  lactis  acidi  is  applied  to  the  typical  representa- 
tive of  the  first  group.  The  natural  habitat  of  this  organ- 
ism is  unknown.  It  is  a  facultative  non-spore-forming  or- 
ganism. Its  optimum  temperature  is  from  86°  to  95°  F. 
It  grows  rapidly  at  from  60°  to  68°  F.,  and  some  strains 
at  50°  F.  Owing  to  its  facultative  nature,  it  grows 
throughout  the  entire  mass  of  milk,  causing  a  uniform 
curdling.  Normally  it  is  not  introduced  into  milk  in  as 
large  numbers  as  many  other  kinds  of  bacteria;  but,  as  it 
finds  in  this  medium  an  exceedingly  favorable  environment, 
it  is  responsible  for  most  of  the  decomposition  that  is  noted 


188  AGRICULTURAL  BACTERIOLOGY 

in  milk.  No  gas  is  formed  by  this  organism.  It  produces 
chiefly  lactic  acid  and  small  quantities  of  volatile  acids, 
such  as  formic  and  acetic.  Other  substances  of  unknown 
nature  are  formed  in  minute  amounts. 

The  effect  of  its  growth  in  milk  is  to  produce  a  jellylike 
curd  that  has  an  agreeable  odor  and  a  mild  acid  taste. 
When  the  curdled  milk  is  shaken,  the  curd  becomes  very 
finely  divided  and  the  milk  assumes  a  creamy  consistency. 
The  milk  fermented  by  this  organism  forms  an  appetizing 
and  healthful  food. 

The  second  group  is  commonly  known  as  B.  coli-aero genes 
group.  The  organisms  are  facultative  and  non-spore-form- 
ing. Some  produce  sufficient  acid  to  curdle  milk;  others 
do  not.  The  chief  characteristic  is  the  formation  of  a  mix- 
ture of  carbon-dioxide  and  hydrogen  in  greater  or  less 
abundance.  The  formation  of  gas  in  curdled  milk  causes 
an  open  or  spongy  curd.  The  milk  in  which  these  organ- 
isms have  grown  usually  has  a  disagreeable  taste  and  odor, 
for  which  reason  they  are  dreaded  by  butter-  and 
cheese-makers. 

The  organisms  of  the  first  group  may  be  said  to  be  de- 
sirable, since  they  protect  the  milk  from  the  action  of 
other  less  desirable  forms  and  are  of  great  value  in  dairy 
manufacturing.  The  coli-aerogenes  organisms  are  "  unde- 
sirable from  every  point  of  view. 

If  the  milk  has  been  produced  with  due  regard  to  cleanli- 
ness, the  lactic  bacteria  will  generally  predominate,  but  if 
quantities  of  manure  and  dirt  find  their  way  into  the  milk, 
the  colon  group  of  bacteria  will  gain  the  ascendency.  It 
is  often  asserted  that  milk  fermented  by  the  colon  group 
of  bacteria  is  unhealthful.  Whether  this  is  true  may  be 
questioned,  but  every  consideration,  both  esthetic  and  eco- 
nomic, demands  that  the  milk  be  produced  under  conditions 
that  will  render  contamination  as  small  as  possible. 


ACID  FERMENTATION  OF  MILK  189 

Only  a  portion  of  the  sugar  of  the  milk  is  fermented  by 
these  acid-forming  bacteria.  The  casein  and  the  ash  con- 
stituents of  the  milk  are  able  to  unite  with  a  certain  amount 
of  acid,  but  as  soon  as  free  acid  appears  in  the  milk  the 
growth  of  these  bacteria  is  checked.  The  amount  of  acid 
normally  formed  ranges  from  0.8  to  1  per  cent. 

The  acid-forming  bacteria  of  milk  are  non-spore-bearing, 
a  fortunate  provision,  since  it  permits  of  the  use  of  the 
pasteurization  process  as  an  aid  in  the  preservation  of 
milk.  Each  of  the  groups  is  able  to  grow  both  in  the  ab- 
sence and  the  presence  of  air — again  a  fortunate  circum- 
stance, otherwise  the  use  of  either  group  in  dairy  manufac- 
turing would  be  impossible. 

Milk  forms  an  excellent  example  of  the  preservative 
action  of  acid  against  putrefaction.  The  increase  of  acid 
due  to  the  lactic  bacteria  quickly  inhibits  the  development 
of  types  capable  of  attacking  the  casein  and  albumen.  As 
long  as  the  milk  remains  sour,  it  is  not  subject  to  the  action 
of  putrefactive  bacteria.  But  usually  there  appears  on  the 
surface  of  the  sour,  raw  milk  in  the  course  of  time  a  white 
mold,  O'idium  lactis,  which  uses  the  acid  by-products  as 
food,  gradually  changing  the  reaction  from  acid  to  alka- 
line. Under  these  conditions  the  putrefactive  bacteria  that 
are  always  present  are  able  to  develop,  and  soon  the  milk 
is  changed  to  a  vile  smelling  mass.  ^lilk  forms  an  excel- 
lent example  of  the  seciuence  of  decomposition  processes  in 
nature  where  one  type  of  life  is  dependent  upon  the  by- 
products formed  by  another  group  of  organisms. 

Representatives  of  another  group  of  acid-forming  bac- 
teria are  found  constantly  in  milk.  The  type  of  organism 
is  usually  called  Bad.  Bulgaricum.  The  members  of  this 
group  are  long  rods  which  often  occur  in  threads  of  con- 
siderable length.  They  do  not  form  spores,  are  facultative, 
and  are  often  classed  as  thermophilic,  since  they  grow  best 


190  AGRICULTURAL  BACTERIOLOGY 

at  110°  to  120°  F.  The  visible  change  that  they  produce 
in  milk  is  identical  with  that  produced  by  the  lactic  bac- 
teria. The  chemical  change  is  also  similar.  These  organ- 
isms form  an  exception  to  bacteria  in  general,  in  that  they 
can  grow  in  rather  acid  solutions.  Owing  to  this  property, 
they  continue  to  grow  after  the  lactic  and  colon  organisms 
have  ceased  to  grow.  They  can  produce  from  1  to  3  per 
cent,  of  acid  in  milk.  They  play  no  part  in  the  souring  of 
milk,  since  they  grow  very  slowly  at  from  60°  to  80°  F. 

These  organisms  play  an  important  role  in  the  ripening 
of  certain  varieties  of  cheese.  They  are  also  widely  used 
in  the  preparation  of  fermented  milks,  either  alone  or  with 
the  lactic  bacteria.  Attention  was  first  directed  to  them 
in  this  connection  by  the  investigations  of  Metchnikoff  in 
regard  to  the  cause  of  senility.  He  believed  it  to  be  due 
to  the  gradual  change  in  the  intestinal  flora  from  one  that 
was  primarily  acid-forming  to  one  in  which  putrefactive 
bacteria  predominated.  His  idea  was  that  this  change 
could  be  prevented  by  the  ingestion  of  the  peculiar  type  of 
fermented  milk  used  by  the  people  of  Bulgaria.  Metchni- 
koff believed  the  Bulgars  are  characterized  by  a  large  num- 
ber of  people  who  attain  an  extreme  age,  a  fact  that  he 
ascribed  to  the  use  of  yoghurt,  the  name  given  to  the  fer- 
mented milk  as  it  is  prepared  in  Bulgaria. 

The  organism  was  isolated,  and  cultures  soon  distributed 
to  all  parts  of  the  world.  Their  use  is  often  recommended 
by  physicians  for  cases  of  digestive  troubles.  It  is  not  at 
all  certain  that  this  particular  type  of  organism  is  more 
valuable  in  this  regard  than  is  the  true  lactic  organism.  In 
fact,  most  of  the  fermented  milk,  commercially  prepared, 
is  made  by  employing  the  two  groups  of  organisms,  which 
are  grown  separately,  and  then  the  fermented  milks  are 
mixed  in  the  desired  proportions.  Bact.  Bulgaricum  gives 
to  the  fermented  milk  a  smooth,  creamy  texture,  which 


ACID  FERMENTATION  OF  MILK  191 

is   sometimes   difficult   to    secure    with    Bad.    lactis   acidi 
alone. 

Buttermilk  and  cottage  cheese  are  to  be  classed  as  types 
of  fermented  milk.  Both  form  excellent  examples  of  a 
material  that  has  undergone  fermentative  changes,  and  yet 
is  a  desirable  and  a  healthful  food.  Milk  in  the  fermented 
form  is  widely  used  in  the  Southern  States  and  in  certain 
tropical  regions  where  it  would  be  difficult  to  keep  it  in  the 
unfermented  condition. 

Sweet  curdling  of  milk. — Sometimes  milk  becomes  seeded 
with  other  organisms  than  the  usual  lactic  type,  and  other 
fermentative  changes  are  produced.  A  common  type  of 
change  that  is  especially  likely  to  occur  in  the  absence  of 
the  lactic  fermentation  is  the  sweet  curdling  change  in 
which  the  casein  and  albumen  are  acted  upon,  the  former 
being  precipitated  in  a  manner  similar  to  that  caused  by 
rennet.  Since  this  change  is  occasioned  by  many  spore- 
forming  organisms,  heated  milks  (sterilized  or  boiled)  are 
peculiarly  prone  to  undergo  this  change.  In  addition  to 
the  curdling  enzymes  analogous  to  rennet,  digestive  en- 
zymes are  also  produced  that  are  similar  in  their  action 
to  trypsin,  which  is  found  in  the  intestinal  juices  of  all  ani- 
mals and  which  changes  protein  materials  to  soluble  prod- 
ucts. The  bacterial  trypsin  gradually  digests  the  curdled 
casein,  so  that  the  change  is  frequently  called  the  digestive 
fermentation  of  milk.  The  digestive  changes  produced  are 
very  similar  to  those  that  take  place'  in  the  decomposition 
of  all  proteins. 

Butjrric  fermentation. — Those  organisms  that  are  able 
to  ferment  sugars  with  the  formation  of  the  volatile  butyric 
acid  are  also  found  in  milk,  and  at  times,  in  the  absence  of 
the  lactic  acid  bacteria,  produce  their  characteristic  fer- 
mentation, which  is  marked  by  the  peculiar  odor  of  the 
acid.     Gas  is  also  produced,  and  in  its  initial  stages  the 


192 


AGRICULTURAL  BACTERIOLOGY 


fermentation  may  be  mistaken  for  one  due  to  the  colon 
group  of  bacteria. 

Slimy  fermentations. — In  sugar  solutions  fermentations 
are  often  noted  that  change  the  solution  into  a  slimy  or 
ropy  liquid.  In  the  manufacture  of 
sugar  the  syrup  may  be  changed  into 
a  mass  almost  jellylike  in  consistency, 
due  to  the  growth  of  bacteria  that 
possess  a  gelatinous  capsule  around 
the  cell.  In  maple  sap  a  ropy  change 
is  often  noted,  and  the  same  is  true  of 
milk. 

This  abnormal  change  seems  to  be 
produced  most  frequently  at  low  tem- 
peratures. In  milk  two  types  of  or- 
ganisms may  be  concerned.  The 
Norwegians  have  long  used  a  fer- 
mented milk  of  this  type  as  a  drink. 
This  prepared  milk,  known  as  taetem- 
jolk,  has  the  taste  of  ordinary  sour 
milk,  but  the  texture  is  more  or  less 
slimy,  depending  on  how  long  the 
fermentation  has  been  allowed  to  pro- 
ceed. The  organism  Bad.  lactis 
longiy  used  in  its  preparation,  is  a 
member  of  the  Bad.  ladis  acidi 
group,  all  of  which  form  a  slight  ropi- 
ness  in  milk.  The  slight  increase  in 
viscosity  caused  thereby  is  desirable 
in  any  fermented  milk  that  is  to  be 
used  as  food,  since  such  change  pre- 
vents the  settling  of  the  curd  and  the  appearance  of  the  free 
whey,  which  imparts  to  the  milk  an  unappetizing  appear- 
ance. 


Fig.  40.  Ropy  Milk 
It  may  be  drawn  out  into 
long  threads  and  does  not 
mix  with  water  when 
poured  into  it  as  does 
milk  that  has  undergone 
a  more  normal  type  of 
decomposition 


ALCOHOLIC  FERMENTATION  193 

The  second  group  of  bacteria  that  produce  a  ropy  change 
in  milk  are  aerobic,  and  therefore  only  the  upper  layers 
of  the  milk  show  an  abnormal  condition.  It  is  most  com- 
monly noted  in  milk  stored  at  rather  low  temperatures  for 
a  period  of  from  twenty-four  to  thirty-six  hours.  Out- 
breaks of  this  trouble  often  cause  extensive  losses  in  the 
milk-distributing  business.  It  seems  probable  that  uten- 
sils, once  infected,  become  a  constant  source  of  infection  of 
milk.  Remedial  measures  should  always  include  the  thor- 
ough scalding  of  the  utensils.  There  is  no  reason  to  be- 
lieve that  the  milk  in  which  either  of  these  groups  of  or- 
ganisms has  grown  is  in  any  way  unhealthful. 

Various  other  abnormal  fermentations  are  sometimes 
noted  in  milk  when  the  lactic  bacteria  are  replaced  by 
other  groups.  Many  bacteria  produce  colored  by-products, 
and  when  such  organisms  grow  in  milk  to  any  extent  a  color 
may  be  imparted  to  the  same.  The  appearance  of  red  and 
blue  milk  is  thus  explained.  Bitter  milk  may  be  due  to  the 
ingestion  of  feeds  that  contain  a  bitter  principle,  or  to  the 
production  of  soluble  decomposition  products  by  the  putre- 
factive bacteria.  Some  acid-forming  bacteria  produce  bit- 
ter fla'vors. 

Alcoholic  fermentation. — When  fruits  such  as  the  grape 
and  apple  are  pressed,  and  the  juice  allowed  to  undergo 
spontaneous  decomposition,  the  sugar  will  be  fermented 
with  the  production  of  alcohol  and  carbon-dioxide.  This 
fermentation  is  due  to  the  yeasts  that  are  present  on  the 
fruit,  having  been  carried  there  from  the  soil  by  dust  and 
insects.  Any  rupture  of  the  skin  allows  the  juice  to  exude, 
and  thus  the  growth  of  yeast  on  unpicked  fruit  is  possible. 
The  juice  is  more  heavily  seeded  with  bacteria  and  molds 
than  it  is  with  yeasts.  The  acidity  of  the  juice  is  suflfi- 
eiently  high  to  prevent  the  growth  of  most  bacteria;  the 
molds  do  not  find  so*  favorable  an  environment  as  do  the 


194  AGRICULTURAL  BACTERIOLOGY 

yeasts,  and  hence  these  organisms  are  certain  to  dominate 
the  fermentation  in  the  fruit  juice. 

The  variety  of  yeast  has  much  to  do  with  the  quality  of 
the  wine  or  cider  that  is  secured.  The  sugar  is  not  changed 
wholly  into  the  two  products  named,  but  other  substances 
are  formed  which  influence  the  flavor  of  the  product. 

In  the  making  of  fermented  and  distilled  liquors,  such  as 
beer  and  whisky,  and  in  the  manufacture  of  industrial  alco- 
hol, starch  is  used.  This  is  changed  into  maltose  by  the 
enzymes  of  the  malt,  which  is  prepared  by  allowing  barley 
to  sprout.  In  this  process  the  enzyme  is  formed  in  such 
abundance  that  a  small  amount  of  malt  can  be  used  to  con- 
vert the  starch  of  a  much  larger  amount  of  grain  into 
maltose,  which  is  easily  fermented  by  yeasts.  The  liquid 
to  be  fermented  will  not  contain  sufficient  yeasts  to  insure 
rapid  fermentation.  It  is  also  a  favorable  medium  for 
many  kinds  of  bacteria.  In  order  to  avoid  trouble  there- 
from, it  is  necessary  to  heat  the  liquid  to  free  it  from  bac- 
teria, and  then  to  seed  it  heavily  with  selected  yeasts.  The 
variety  of  organism  that  ferments  the  sugar  will  have 
much  to  do  with  the  flavor  of  the  finished  product.  This  is 
of  especial  importance  in  the  manufacture  of  beer.  In 
the  manufacture  of  distilled  liquors  and  industrial  alcohol, 
it  is  essential  to  employ  a  yeast  that  will  be  capable  of  pro- 
ducing large  amounts  of  alcohol  before  it  is  inhibited 
thereby. 

The  growth  of  harmful  types  of  bacteria  in  the  material 
to  be  subjected  to  alcoholic  fermentation  may  be  prevented 
by  inoculating  it  with  certain  lactic-acid-forming  bacteria. 
The  acid  formed  by  them  will  not  influence  the  growth  of 
the  yeast,  and  since  but  traces  of  volatile  acid  are  formed, 
the  quality  of  the  distillate  from  the  fermented  liquor  will 
not  be  unfavorably  influenced  by  the  acid  formed  in  the 
fermented  material. 


ALCOHOLIC  FERMENTATION  195 

The  alcoholic  fermentation  does  not  occur  normally  in 
milk,  because  lactose,  the  sugar  in  milk,  is  not  readily  sus- 
ceptible to  fermentation.  Also,  the  extent  of  seeding  with 
yeasts  is  not  sufficient  to  enable  fermentative  changes  to 
develop  rapidly.  As  a  consequence,  the  activity  of  the 
yeasts  is  usually  overshadowed  by  bacterial  changes. 
While  most  yeasts  are  unable  to  act  on  milk-sugar,  yet 
lactose-fermenting  yeasts  do  occur  not  infrequently,  and 
are  often  to  be  noted  in  milk  if  it  is  held  for  some  time 
after  it  has  become  sour.  The  soured  milk  will  contain 
an  abundance  of  sugar,  and  the  acid  will  prove  no  de- 
terrent to  yeast  growth.  Yeast  development  occurs  in  milk 
and  cream  held  for  considerable  periods.  Cream  supplied 
to  large  centralized  creameries  often  shows  a  yeasty  fer- 
mentation. An  alcoholic  fermentation  is  also  noted  in 
cheese  factories,  especially  in  the  whey-tanks,  on  account 
of  the  favorable  opportunity  for  contamination  and  growth 
of  yeasts. 

When  such  fermented  whey  is  returned  to  the  farm  in 
milk-cans  and  these  are  imperfectly  washed,  the  fresh  milk 
may  become  seeded  to  such  an  extent  as  to  cause  abnormal 
fermentations  in  the  cheese,  injuring  its  commercial  value. 
This  is  particularly  true  of  Swiss  cheese,  in  which  the  de- 
velopment of  acid  in  the  process  of  making  is  not  carried 
sufficiently  far  to  transform  all  of  the  sugar  into  acid. 

Certain  kinds  of  fermented  milks  are  also  prepared  by 
the  use  of  lactose-fermenting  yeasts.  When  raw  milk  is 
used,  the  milk  will  be  subject  to  both  the  acid  and  the  alco- 
holic fermentations,  and  the  taste  of  the  acid  milk  will  be 
modified  by  that  of  the  alcohol.  Two  of  these  fermented 
milks  are  widely  used  in  eastern  Europe  and  western  Asia. 
Koumiss  is  prepared  from  mare's  milk  by  the  nomadic 
peoples  of  the  Caucasus.  The  fresh  milk  is  inoculated  with 
a  little  of  the  previously  fermented  milk,  which  may  be 


196  AGRICULTURAL  BACTERIOLOGY 

dried  when  it  is  desired  to  keep  it  for  long  periods.  The 
drink  contains  about  2  per  cent,  of  alcohol  and  1  per  cent, 
of  acid.  It  has  been  introduced  into  western  Europe  and 
America  because  of  its  supposed  therapeutic  value  in  the 
treatment  of  tuberculosis,  and  for  typhoid-fever  conva- 
lescents. An  artificial  koumiss  is  sometimes  prepared  by 
adding  cane-sugar  to  cow's  milk  and  seeding  it  with  ordi- 
nary yeast. 

Kefir  is  another  drink  prepared  from  milk  by  inoculating 
the  milk  with  Kefir  grains,  which  consist  of  masses  of 
yeasts  and  bacteria.  The  grains  are  dried  and  may  be 
bought  as  articles  of  commerce.  The  composition  of  kefir 
is  similar  to  that  of  koumiss,  except  that  the  content  of 
alcohol  is  less.  These  drinks  have  been  largely  supplanted 
in  this  country  by  yoghurt,  which  is  prepared  by  the  use 
of  the  Bad.  Bulgaricum. 

Manufacture  of  vinegar.— Ethyl  or  grain  alcohol,  as  it 
is  often  called  to  distinguish  it  from  methyl  or  wood  alco- 
hol, furnishes  a  source  of  food  and  energy  for  a  class  of 
bacteria  that  are  known  as  the  acetic  acid  bacteria,  since 
they  oxidize  alcohol  to  acetic  acid.  If  cider,  wine,  or  a 
similar  liquid  containing  alcohol  is  exposed  to  the  air,  it 
soon  becomes  covered  with  a  whitish  or  gray  film,  or  mem- 
brane, and  the  alcohol  is  gradually  changed  to  acetic  acid. 
The  term  vinegar  is  applied  to  the  product  thus  obtained. 
If  the  film,  which  consists  of  masses  of  bacteria,  is  allowed 
to  remain  undisturbed,  the  liquid  remains  clear.  If  it  is 
disturbed,  the  particles  of  membrane  sink  to  the  bottom, 
and  the  surface  soon  becomes  covered  with  a  fresh  film. 
The  film,  which  is  known  as  mother  of  vinegar,  may  increase 
in  thickness,  and  finally  present  the  appearance  of  a 
leathery  mass.  The  acetic  acid  formation  can  go  on  only 
under  aerobic  conditions,  since  the  organisms  concerned  in 


VINEGAR  197 

it  must  have  access  to  the  free  oxygen  of  the  air  to  convert 
the  alcohol  into  vinegar.  If  the  alcoholic  liquid  is  kept  in 
closed  or  completely  filled  containers,  the  process  does  not 
occur.  In  the  presence  of  too  large  quantities  of  alcohol, 
above  14  per  cent.,  the  acetic  bacteria  can  not  grow,  and 
the  alcohol  is  not  attacked. 

The  juice  of  most  fruits  contains  sufficient  sugar  so  that, 
after  the  juice  has  undergone  the  alcoholic  fermentation, 
it  can  be  used  successfully  for  the  preparation  of  vinegar. 
The  quality  of  the  vinegar  will  depend  on  the  source  of  the 
juice.  The  vinegars  made  from  wine  and  cider  are  most 
highly  prized  for  table  use  where  the  vinegar  is  used  as  a 
condiment,  since  they  contain  many  organic  acids  atnd 
esters,  derived  from  the  fruits  and  formed  in  the  fermen- 
tation, not  found  in  vinegars  derived  from  other  sources. 
The  flavor  of  these  vinegars  is  therefore  not  simply  that  of 
a  solution  of  acetic  acid.  Most  of  the  vinegar  used  in  the 
preparation  of  pickles  commercially  is  distilled  vinegar  in 
which  the  alcohol  is  obtained  from  the  fermentation  of 
hydrolyzed  starch.  This  vinegar  has  no  flavor  other  than 
that  of  the  acetic  acid.  In  the  pickling  industry  the  pre- 
servative action  of  the  vinegar  is  the  important  thing, 
rather  than  its  flavor. 

On  the  farm  the  vinegar  is  most  often  prepared  from 
apple  cider.  It  is  necessarj-  that  an  abundant  supply  of 
air  be  furnished  to  the  organism,  and  that  the  surface  of 
the  liquid  be  large  in  proportion  to  its  volume.  These  con- 
ditions are  secured  when  a  barrel  is  used  in  which  the  alco- 
holic liquid  is  to  be  changed  to  a  solution  of  acetic  acid. 
The  barrel  should  be  filled  from  one  half  to  two  thirds  full, 
and  then  placed  on  its  side.  The  circulation  of  air  through 
the  barrel  can  be  facilitated  if  openings  are  made  in  the 
barrel-heads  just  above  the  level  of  the  liquid.     To  prevent 


198  AGRICULTURAL  BACTERIOLOGY 

the  entrance  of  fli&s,  these  holes  should  be  screened  with 
thin  cloth  or  with  wire  netting  that  has  been  varnished  so 
that  the  iron  will  not  be  attacked  by  the  acetic  acid.  The 
addition  at  the  start  of  a  small  quantity  of  vinegar,  or  bet- 
ter some  of  the  mother  of  vinegar,  serves  to  seed  the  liquid 
with  the  necessary  acetic  bacteria.  The  fermentative  proc- 
ess progresses  rather  slowly  at  first,  but  in  a  few  months 
the  vinegar  will  be  ready  for  use.  If  it  is  desired  to  con- 
tinue the  process  in  the  same  barrel,  fresh  alcohol  can  be 
added  through  the  bung-hole  by  means  of  a  glass  funnel 
to  which  a  rubber  tube  is  attached.  This  enables  the  alco- 
hol to  be  added  without  disturbing  the  bacterial  film  on  the 
surface. 

Temperatures  between  65°  and  75°  F.  are  most  favorable 
for  both  alcoholic  and  acetic  fermentation.  At  much  lower 
temperatures  the  alcohol  is  produced  so  slowly  that  unde- 
sirable organisms  have  opportunity  for  growth.  When  the 
acetic  fermentation  is  complete,  it  is  desirable  to  protect 
the  acid  from  the  action  of  organisms  that  would  destroy  it. 
This  can  be  done  by  storing  it  in  completely  filled  and 
closed  containers,  for  all  harmful  organism  will  be  of  the 
aerobic  group. 

Under  the  best  of  conditions  the  oxidation  of  the  alcohol 
to  acetic  acid  will  require  a  long  period  in  the  method  de- 
scribed, since  the  growth  of  the  organism  is  confined  to  the 
surface  of  the  liquid.  In  the  manufacture  of  distilled  vine- 
gar, the  oxidation  process  is  hastened  by  providing  a  much 
extended  surface  for  the  growth  of  the  bacteria  and  by  pro- 
viding for  a  constant  supply  of  air  to  the  organisms. 
These  conditions  are  secured  by  filling  large  conical  tanks 
with  beech  shavings  that  have  been  extracted  with  water 
and  with  vinegar.  The  tank  has  a  false  bottom  containing 
numerous  holes  for  the  passage  of  air,  which  enters  the 
tank  through  holes  in  its  side  below  the  false  bottom. 


BREAD  199 

The  alcoholic  liquid  is  sprinkled  on  the  surface  in  such 
a  way  that  it  will  be  evenly  distributed  over  the  shavings, 
which  soon  become  covered  with  bacterial  growth.  The 
fermentative  process  produces  lieat,  and  hence  there  is  a 
constant  current  of  air  through  tlie  holes  at  the  bottom  of 
the  cask.  The  air  passes  upward  through  the  shavings  and 
out  at  the  top.  In  this  manner  the  bacteria  are  provided 
with  an  abundant  supply  of  air  facilitating  the  oxidation 
process.  As  fresh  food  is  constantly  supplied  and  as  the 
by-products  of  the  fermentation  are  also  constantly  re- 
moved, the  change  goes  on  continuously  and  with  rapidity. 

It  is  essential  that  the  alcoholic  solution  does  not  contain 
too  much  nitrogenous  food,  since  this  would  so  accelerate 
the  growth  of  bacteria  as  to  fill  the  interstices  with  bacteria 
and  cause  a  consequent  reduction  of  the  flow  of  air  through 
the  shavings.  It  is  essential  that  the  mass  of  bacterial 
growth  be  kept  in  a  healthy  and  active  condition,  so  that 
the  cells  shall  exert  their  oxidizing  action  rapidly.  Usually 
the  liquid  is  passed  through  a  series  of  three  tanks  situated 
one  above  the  other.  By  the  time  it  flows  from  the  last 
tank,  the  oxidation  will  be  sufficiently  complete. 

Bread. — The  making  of  bread  represents  another  fer- 
mentation industry  that  is  carried  out  in  many  homes.  If 
flour,  water,  a  small  amount  of  salt,  and  fat,  such  as  lard 
or  butter,  are  mixed  and  baked,  a  dense  hard  mass  is  ob- 
tained, such  as  a  cracker  or  unleavened  bread.  If,  however, 
yeast  is  added  to  the  mixture,  and  the  dough  placed  under 
conditions  that  permit  the  yeast  to  grow,  the  sugar  is 
changed  into  alcohol  and  carbon-dioxide.  The  dough  made 
from  such  flours  as  wheat  contains  gluten,  which  imparts 
a  plasticity  to  the  mass.  As  the  gas  is  formed,  it  is  unable 
to  escape  readilj^  from  the  dough,  and  the  whole  mass 
*' rises,''  producing  the  "sponge"  which  characterizes  all 
leavened  breads.     When  the  gas  is  heated  in  the  baking 


200  AGRICULTURAL  BACTERIOLOGY 

process,  further  expansion  occurs,  and  the  loaf  becomes 
light  and  porous.  The  yeast  may  be  obtained  by  saving 
a  piece  of  the  dough  from  the  previous  baking,  by  the  pur- 
chase of  dried  or  compressed  yeast,  or  by  furnishing  con- 
ditions favorable  to  the  natural  seeding  of  the  materials. 

The  leaven  most  commonly  used  is  compressed  yeast. 
The  yeast  is  secured  by  seeding  a  maltose  solution,  as  in 
the  manufacture  of  alcohol,  with  a  pure  culture  of  yeast. 
Air  is  passed  through  the  solution  for  from  six  to  eight 
hours.  The  thorough  aeration  results  in  an  increased 
growth  of  yeast.  The  cells  are  removed  by  centrifugation, 
washed,  and  pressed. 

In  the  baking  industry  large  quantities  of  compressed 
yeast  are  added  to  the  dough,  and  the  rising  takes  place 
rapidly.  If  smaller  amounts  of  yeast  are  used,  as  is  usual 
in  the  home,  a  longer  time  must  be  allowed  for  the  growth 
of  the  yeast  and  the  formation  of  sufficient  gas  to  produce 
the  desired  porosity  in  the  bread.  In  this  case  the  yeast  is 
added  to  a  thin  mixture  of  flour  and  water,  called  the  bat- 
ter. After  standing  for  a  few  hours  in  a  warm  place,  ad- 
ditional flour  is  added,  and  the  yeast  uniformly  incorpo- 
rated with  the  dough  by  the  kneading  process.  More  or 
less  bacterial  growth  takes  place  in  the  dough,  depending 
on  the  length  of  time  it  is  allowed  to  stand  before  baking. 
The  bacteria  have  much  to  do  with  the  flavors  of  the  bread. 
If  the  development  of  the  bacteria  has  been  too  great,  the 
bread  is  likely  to  have  an  acid  or  sour  taste. 

If  no  yeast  is  added,  but  the  mixture  of  flour  and  water 
is  allowed  to  stand,  gas  will  be  produced  by  the  gas-forming 
bacteria  that  are  normally  in  the  flour.  The  yeasts  that  are 
naturally  present  will  also  function.  Such  bread  has  a 
quite  different  flavor  from  the  ordinary  product,  and  is 
called  salt-rising  bread.  The  flavor  is  far  from  constant, 
since  there  is  no  control  over  the  kind  of  organisms  that 


BREAD  201 

grow  in  the  mass.  Studies  made  during  recent  years  point 
to  the  use  of  pure  cultures  of  bacteria  in  the  manufacture 
of  salt-rising  bread,  and  to  a  better  control  of  the  flavor  of 
the  product. 

Bread  and  other  bakery  goods  are  not  likely  to  undergo 
decomposition  changes  to  any  great  extent,  as  ordinarily 
they  are  consumed  in  a  fresh  state.  If  kept  in  a  damp 
place,  mold  soon  appears  on  the  surface.  In  the  baking 
process  the  vegetative  bacteria  are  readily  destroyed,  but 
the  spores  resist.  At  times,  especially  in  warm  weather, 
bread  and  cake  may  undergo  a  slimy  fermentation,  due  to 
the  growth  of  the  spores  of  certain  kinds  of  bacteria  that 
may  be  present  in  either  the  flour  or  the  yeast. 


CHAPTER  XVII 

THE  RELATION  OF  MICROORGANISMS  TO 
BUTTER  AND  CHEESE 

The  preparation  of  condensed  milk  and  milk  powder  rep- 
resents a  method  of  conserving  milk  in  a  less  bulky  form 
than  the  original  product,  a  great  advantage  when  it  is  to 
be  transported  for  long  distances.  The  manufacture  of 
butter  represents  a  method  of  concentrating  the  butter  fat 
of  the  milk,  while  in  cheesemaking  the  fat  and  the  casein, 
together  with  a  small  part  of  the  milk  serum,  are  concen- 
trated. 

It  is  essential  that  the  butter  and  cheese  shall  possess  cer- 
tain physical  and  chemical  properties.  Most  important 
among  these  properties  is  the  flavor.  The  flavor  of  foods 
is  very  important,  an  agreeable  odor  and  pleasant  taste  in 
any  food  making  it  much  more  appetizing,  if  not  influ- 
encing its  nutritive  value.  The  use  of  condiments  and 
flavoring  substances  of  all  kinds  in  many  foods  is  evidence 
of  the  value  of  flavor  in  foods. 

If  cream  is  separated  from  sweet,  fresh  milk,  and  the 
remaining  part  of  the  milk  serum  is  eliminated  by  the 
churning  process,  the  butter  thus  obtained  will  be  devoid 
of  flavor,  and,  to  those  accustomed  to  butter  made  from 
cream  that  has  been  allowed  to  sour  before  being  churned, 
it  is  not  at  all  attractive.  Sweet-cream  butter  is  made  in 
all  the  countries  of  southern  Europe,  while  that  from  fer- 
mented cream  is  made  in  northern  Europe,  America,  Aus- 
tralia, Asia,  and  South  America.  Sour  or  acid  cream  but- 
ter, therefore,  represents  the  great  mass  of  the  butter  sup- 
ply of  the  world. 

202 


BUTTER  203 

Acid-fermentation  and  flavor  of  butter. — As  earlier  set 
forth,  two  groups  of  acid-forming  bacteria  are  concerned  in 
the  souring  of  milk.  The  lactic  group  tends  to  predominate 
in  milk  that  is  produced  under  clean  conditions,  since  it 
grows  more  rapidly  at  ordinary  temperatures  than  does  the 
colon  group,  which,  by  reason  of  the  products  formed,  in- 
jures the  taste  and  odor  of  the  milk,  and  hence  the  flavor  of 
the  butter.  In  the  lactic  fermentation  not  only  is  lactic 
acid  produced,  but  also  other  acids,  alcohols,  and  esters  that 
impart  to  the  sour  milk  and  cream  an  agreeable  odor  and 
taste.  Butter-fat  has  the  power  of  absorbing  some  of  these 
volatile  substances,  just  as  it  will  absorb  the  odors  of  fruits 
when  kept  in  the  same  container  with  them.  The  difference 
in  flavor  between  the  sweet  and  ripened  cream  butter  is, 
therefore,  due  to  the  absorption  of  some  of  these  products 
during  the  ripening  of  the  cream  and  the  churning  process. 
Cream  that  is  allowed  to  sour  spontaneously  will  usually 
contain  many  more  lactic  than  colon  organisms,  and  the 
butter  made  from  it  may  be  of  very  excellent  quality. 

As  long  as  butter  was  made  on  the  individual  farm,  no 
great  need  of  control  was  felt ;  but  as  its  manufacture  be- 
came centralized  in  creameries,  it  became  necessary  to  con- 
trol not  only  the  kind  of  organisms  growing  in  the  cream, 
but  also  the  rate  at  which  the  fermentation  should  go  on. 

The  bacterial  content  of  cream,  both  qualitatively  and 
quantitatively,  will  depend  on  the  method  by  which  the 
milk  has  been  creamed.  If  it  has  been  allowed  to  stand  in 
shallow  vessels  at  the  fluctuating  air  temperatures  and  ex- 
posed to  contamination  from  the  air,  it  will  contain  greater 
numbers  and  more  varied  kinds  of  bacteria  than  if  the 
creaming  takes  place  at  low  temperatures  and  in  covered 
containers.  If  the  centrifugal  separator  is  employed,  the 
bacterial  content  of  the  cream  will  be  similar  in  kind  to 
that  of  milk. 


204  AGRICULTURAL  BACTERIOLOGY 

Control  of  flavor. — The  modern  methods  of  butter-mak- 
ing are  designed  to  give  the  maker  control  over  the  kinds 
of  bacteria  that  are  concerned  in  the  fermentation  of  the 
cream.  The  first  step  in  this  direction  was  to  add  to  the 
cream  selected  pure  cultures  of  lactic  bacteria  that  had 
been  isolated  from  varied  sources,  and  tested  as  to  their 
favorable  flavor-forming  properties  and  their  ability  to 
grow  at  the  ripening  temperatures.  The  organisms  are 
propagated  in  milk  that  has  been  heated  sufficiently  to  de- 
stroy all  of  the  non-spore-forming  bacteria.  This  is  then 
inoculated  with  the  pure  culture  of  lactic  bacteria.  If  the 
butter-maker  exercises  care  in  the  prevention  of  contamina- 
tion and  in  the  control  of  the  temperature  at  which  it  is 
kept,  this  pure  culture  starter  can  be  maintained  for  a 
long  period  of  time.  He  is  thus  in  a  position  to  grow  the 
desirable  organism  in  any  quantity,  for  addition  to  the 
cream  that  is  to  be  fermented  or  ripened. 

The  lactic  bacteria  are  quite  resistant  to  desiccation. 
The  commercial  laboratories  make  use  of  this  property,  and 
market  the  pure  cultures  of  the  organism,  not  only  in  milk, 
but  in  a  dried  condition.  These  are  usually  prepared  by 
adding  the  fermented  milk  to  a  relatively  large  amount  of 
some  inert  substance,  such  as  milk  sugar  or  milk  powder, 
and  drying  the  mass  at  a  low  temperature.  The  organisms 
remain  alive  in  this  condition  much  longer  than  where  they 
are  exposed  to  their  by-products,  as  in  milk. 

Pasteurization  of  cream. — If  the  starter  is  added  to  raw 
cream,  its  effect  will  depend  on  the  number  of  bacteria 
present  in  the  cream.  If  the  cream  is  sweet  and  clean,  the 
number  of  bacteria  added  in  the  starter  will  greatly  ex- 
ceed those  naturally  found  in  the  cream,  and  the  fermenta- 
tion will  be  largely  due  to  the  added  bacteria.  If,  however, 
the  cream  is  nearly  sour  from  the  bacteria  already  present, 
the  fermentation  may  not  be  much  influenced  by  the  starter. 


BUTTER  205 

In  order  to  obtain  the  maximum  effect  and  to  give  the  or- 
ganisms added  in  the  starter  a  clear  field,  it  is  advisable 
to  pasteurize  the  cream  and  then  add  the  starter.  In  the 
pasteurizing  process  the  acid-forming  bacteria  will  be  de- 
stroyed, and  the  entire  fermentation  will  be  controlled  by 
the  added  bacteria.  By  the  use  of  this  method,  the  butter- 
maker  has  entire  control  over  the  flavor  of  the  product, 
provided  he  is  furnished  with  a  good  quality  of  raw  mate- 
rial, i.  e.,  sweet,  fresh,  clean  cream. 

The  ripening  of  the  cream  also  aids  in  the  churning  proc- 
ess, causing  the  cream  to  churn  more  quickly,  and  diminish- 
ing the  loss  of  butter-fat  in  the  milk.  The  ripening  of  the 
cream  also  improves  the  keeping  quality  of  the  butter  made 
from  raw  cream.  It  is  probable  that  if  the  butter  is  made 
from  pasteurized  cream  the  sweet-cream  butter  has  better 
keeping  qualities.  The  pasteurization  also  destroys  any 
pathogenic  bacteria  that  may  be  present  in  the  cream.  * 

The  control  of  the  ripening  of  the  cream  is  desirable 
from  the  standpoint  of  the  rapidity  with  which  the  process 
goes  on.  The  flavor  of  the  product  will  depend  on  the 
degree  of  acidity  developed  in  the  cream,  or,  in  other  words, 
on  the  relative  amounts  of  flavoring  substances  and  butter- 
fat.  If  the  cream  is  low  in  fat,  the  same  amount  of  flavor- 
ing substances  will  impart  to  the  butter  a  higher  degree  of 
flavor  than  if  there  had  been  twice  as  much  fat  in  the 
cream.  It  is,  therefore,  desirable,  from  the  standpoint  of 
the  control  of  the  degree  of  flavor,  to  stop  the  development 
of  acid  when  it  has  reached  the  proper  point.  Also  from 
the  standpoint  of  convenience  it  is  desirable  to  have  the 
cream  ripened  at  that  rate  which  will  make  possible  the 
churning  at  about  the  same  hour  each  day.  This  can  be 
accomplished  by  varying  the  amount  of  starter,  and  by  the 
control  of  the  temperature  at  which  the  cream  is  kept. 

Starters  are  rarely  used  on  the  farm.    It  is  certain  that 


206  AGRICULTURAL  BACTERIOLOGY 

a  great  improvement  in  farm  butter  could  be  made  by  a 
more  perfect  control  of  the  ripening  process,  which  could 
be  easily  attained  by  the  use  of  starters.  Small  quantities 
of  starters  can  be  made  in  such  vessels  as  fruit-jars  or 
milk-bottles. 

Flavor  of  butter  substitutes. — Oleomargarin  is  made 
from  fats  that  are  devoid  of  butter  flavor.  If  this  product 
is  to  be  sold  as  a  butter  substitute,  the  butter  flavor  must  be 
developed.  This  is  imparted  to.  the  product  by  churning 
the  fats  with  sour  milk.  The  flavor  of  the  oleomargarin 
is  thus  identical  in  origin  and  nature  with  the  flavor  of 
butter.  Renovated  butter  is  made  from  a  poor  quality 
of  butter,  the  flavor  of  which  is  of  low  grade  or  decidedly 
below  standard.  The  fat  used  in  its  manufacture  is 
melted,  and  the  obnoxious  flavors  are  removed  by  passing 
air  through  it,  and  by  washing  the  fat.  The  desirable 
flavor  is  then  imparted  by  churning  the  fat  with  some 
milk  soured  by  pure  cultures  of  bacteria.  In  the  manu- 
facture of  oleomargarin  and  renovated  butter,  the  most 
approved  scientific  methods  are  employed  to  impart  to  the 
otherwise  neutral  fats  the  characteristic  flavor  that  is  so 
much  in  demand  in  the  butter  market. 

Decomposition  of  butter. — Butter  deteriorates  more  or 
less  rapidly,  depending  on  the  kinds  of  bacteria  present  in 
the  cream  and  on  the  temperature  at  which  it  is  stored. 
The  best  keeping  butter  is  that  made  from  sweet  cream  that 
has  been  pasteurized;  the  poorest  keeping  butter  is  that 
from  a  raw,  sweet  cream  or  from  a  sour  cream  that  contains 
not  only  great  numbers  of  undesirable  flavor-forming  bac- 
teria, but  yeasts  and  molds.  If  the  butter  is  stored  at 
ordinary  temperatures,  the  development  of  undesirable 
flavors  is  rapid,  while  at  the  temperatures  maintained  in 
butter-storage  rooms,  below  zero  F.,  the  changes  are  very 
slow.     If  the  butter  is  kept  in  small  packages,  so  that  a 


CHEESE  207 

considerablo  surface  is  exposed  to  the  air,  the  spoiling  will 
be  more  rapid  than  if  the  package  is  larger  or  if  the  butter 
is  hermetically  sealed. 

Abnormal  flavors  in  butter. — Various  abnormal  flavors 
are  noted  in  butter.  These  may  be  due  to  feed,  to  absorp- 
tion of  odors  by  the  milk  or  cream,  or  to  bacterial  by-prod- 
ucts. The  action  of  the  bacteria  may  ])e  indirect,  as  in  the 
case  of  the  "fishy"  flavor  in  butter  which  is  probably  due 
to  the  presence  of  small  quantities  of  iron  or  copper  dis- 
solved from  utensils  by  the  acid  of  the  cream.  The  small 
amount  of  metal  acts  as  a  catalytic  agent,  accelerating  to  a 
marked  degree  some  of  the  decomposition  changes.  All 
vessels  should  be  well  tinned,  so  that  no  solvent  action  can 
be  exerted  by  the  acid. 

Cheese-making. — In  the  making  of  cheese  it  is  necessary 
for  the  casein  and  the  fat  to  be  separated  from  the  milk 
serum.  This  separation  is  accomplished  by  allowing  the 
milk  to  sour,  or  by  the  addition  of  rennet  to  it.  The  latter 
is  the  method  used  in  the  making  of  all  the  varieties  of 
cheese  that  are  of  much  commercial  importance.  Cottage 
or  sour-milk  cheese  is  made  by  allowing  the  milk  to  undergo 
an  acid  fermentation.  It  is  ready  for  use  as  soon  as  the 
whey  has  been  drained  from  it,  and  represents  a  form  of 
fermented  milk. 

The  rennet  cheese  has  no  particular  flavor  at  the  time  it 
is  made,  and  moreover  is  rather  indigestible.  It  is  essen- 
tial that  the  green  cheese  be  allowed  to  undergo  a  ripening 
process  in  which  are  formed  the  peculiar  flavors  that  char- 
acterize the  various  types.  This  process  also  renders  the 
cheese  more  easily  digested.  Bacteria  and  other  micro- 
organisms function  in  the  ripening  of  the  dift'erent  varieties 
of  cheese,  which  vary  greatly  in  texture  and  in  fl.avor.  The 
important  commercial  varieties  of  cheese  are  all  made  from 
the  same  raw  materials,  cow's  milk,  rennet,  and  salt;  but 


208  AGRICULTURAL  BACTERIOLOGY 

variations  in  the  methods  of  manufacture,  and  in  the  con- 
ditions under  which  the  ripening  takes  place,  permit  the 
growth  of  different  classes  of  bacteria  in  the  different  types 
of  cheese. 

The  amount  of  whey  allowed  to  remain  in  the  cheese  will 
cause  a  difference  not  only  in  moisture,  but  also  in  sugar, 
and  hence  in  the  acidity  of  the  product,  since  all  of  the 
sugar  will  be  fermented  by  the  acid-forming  bacteria  of  the 
milk,  which  in  large  part  are  retained  in  the  curd.  The 
type  of  cheese,  such  as  the  Camembert  and  Brie,  in  which 
a  large  amount  of  whey  is  left  is  called  soft  cheese;  those 
from  which  the  whey  is  more  completely  expressed,  as 
represented  by  the  Cheddar  and  Swiss  types,  are  called 
hard  cheese.  The  latter  are  usually  made  in  considerably 
larger  sizes,  and  in  the  case  of  the  American  or  cheddar 
cheese  may  be  made  of  any  desired  size.  In  the  case  of  the 
soft  cheese,  the  ripening  is,  in  part,  due  to  the  action  of 
organisms  that  grow  on  the  surface  of  the  cheese,  and  act 
on  the  curd  by  the  secretion  of  soluble  enzymes  that  diffuse 
into  the  cheese.  If  the  cheese  is  too  large,  the  outer  layers 
will  be  ripe  before  the  inner  portions,  and  the  softness 
makes  the  handling  of  large  cheese  impossible. 

Cheddar  cheese. — In  the  making  of  cheddar  cheese,  the 
most  common  variety  made  in  America,  it  is  essential  that 
the  milk  contain  great  numbers  of  lactic  bacteria,  since  it 
is  necessary  that  a  relatively  large  amount  of  acid  be 
formed  during  the  making  of  the  cheese.  If  the  milk  is  too 
sweet,  or,  in  other  words,  too  low  in  bacteria,  the  maker 
adds  a  starter  prepared  from  pure  cultures  of  lactic  bac- 
teria, just  as  the  butter-maker  does  for  the  control  of  the 
cream-ripening  process.  The  action  of  the  rennet  that  is 
used  to  curdle  the  casein  is  also  facilitated  by  the  acid 
reaction  of  the  milk.  Within  a  few  minutes  from  the  time 
the  rennet  is  added  the  milk  curdles,  and  as  soon  as  it  is 


CHEESE  209 

properly  set,  it  is  cut  into  small  pieces  for  the  purpose  of 
facilitating  the  expulsion  of  the  whey.  With  the  develop- 
ment of  acid,  a  certain  action  is  exerted  on  the  casein,  which 
causes  the  pieces  of  curd  to  adhere  to  each  other,  and  to  fuse 
into  one  mass  under  the  influence  of  the  pressure  exerted  in 
the  press  in  which  the  curd  is  placed  after  the  whey  has 
been  largely  removed.  Bacterial  growth  in  the  curd  occurs 
rapidly,  the  colonies  developing  in  a  manner  similar  to  those 
obtained  in  the  plate  cultures  of  the  bacteriologist. 

The  rennet  used  also  contains  the  digestive  enzyme  of 
the  stomach  juice,  pepsin,  which  can  exert  its  action  only 
in  the  presence  of  an  acid.  In  the  stomach  of  an  animal, 
the  hydrochloric  acid  secreted  by  the  stomach  wall  is  the 
activating  agent,  while  in  the  cheese  the  lactic  acid  formed 
in  the  acid  fermentation  of  the  sugar  gives  favorable  con- 
ditions for  action.  The  protein  of  the  cheese  is  changed 
into  soluble  decomposition  products  similar  to  those  formed 
in  the  stomach  digestion  of  nitrogenous  compounds.  The 
acid  reaction  established  by  the  lactic  bacteria  serves  to 
protect  the  cheese  from  the  action  of  the  putrefactive  bac- 
teria that  are  always  present,  in  the  same  manner  as  the 
acid  of  silage  protects  it  against  putrefaction.  It  is  evi- 
dent that  without  the  lactic  bacteria  the  cheese  will  either 
remain  in  the  same  condition  in  which  it  is  when  removed 
from  the  press,  or  else  it  will  undergo  putrefaction.  It  is 
also  evident  that  without  the  bacteria  the  manufacture  of 
cheese  would  be  impossible. 

Gassy  cheese. — If  the  milk  is  handled  in  such  a  way  as 
to  allow  the  colon  or  gas-forming  type  of  bacteria  to  over- 
come the  usual  lactic  type,  the  quality  of  the  cheese  will 
be  injured,  owing  not  only  to  the  impairment  of  the  flavor 
by  the  by-products  of  these  organisms,  but  the  texture  of 
the  cheese  is  rendered  open  or  porous  by  the  development 
of  gas  which  permeates  the  mass  of  the  cheese. 


210  AGRICULTURAL  BACTERIOLOGY 

The  cheese-maker  can  not,  of  course,  test  the  milk  of  the 
different  patrons  of  liis  factory  for  ^as-forming  bacteria 
by  the  methods  employed  by  the  bacteriologist.  He  can, 
however,  gain  an  idea  of  the  quality  of  the  raw  product  by 
making  what  is  known  as  a  curd  test,  in  which  a  small  por- 
tion of  each  patron's  supply  is  curdled  with  rennet,  after 
which  the  curd  is  broken  up  so  as  to  expel  the  whey,  which 
is  then  turned  off.  The  small  mass  of  curd  is  kept  for  sev- 
eral hours  at  temperatures  that  favor  the  growth  of  the 
gas-forming  bacteria,  100°  to  104°  F.  The  quality  of  the 
milk  is  then  determined  by  the  appearance  of  the  curd  with 
reference  to  the  presence  of  gas-holes;  the  flavor  and  odor 
are  also  noted.  This  rough  qualitative  test  is  of  great  serv- 
ice to  the  cheese-maker  in  detecting  the  quality  of  the  raw 
material.  All  of  the  operations  must  be  carried  out  with 
due  regard  to  contamination  from  outside  sources,  since  it 
is  essential  that  the  changes  noted  in  the  curd  be  caused 
only  by  the  bacteria  in  the  milk,  and  not  by  those  intro- 
duced by  the  use  of  unclean  utensils. 

The  growth  of  mold,  which  occurs  readily  on  the  surface 
of  the  cheese  and  which  is  objectionable  on  account  of  dis- 
coloring the  surface,  can  be  easily  prevented  by  dipping 
the  cheese  in  melted  paraffin.  The  impervious  layer  thus 
formed  excludes  the  air,  thereby  preventing  the  growth  of 
mold  spores. 

Swiss  cheese. — Swiss  cheese  is  made  from  sweet  milk 
that  contains  only  small  numbers  of  lactic  bacteria.  The 
rennet  used  to  curdle  the  milk  is  obtained  from  natural 
"rennets,"  i.e.,  portions  of  dried  calves'  stomachs,  which 
are  soaked  in  whey  and  kept  at  a  temperature  of  from 
80°  to  95°  F.  for  from  twenty-four  to  thirty-six  hours. 
The  whey  contains  numerous  lactic  bacteria,  and  on  the 
dried  rennets  there  are  always  organisms  of  the  Bact, 
Bulgaricum.  type.     This  serves  as  a  starter  to  inoculate  the 


CHEESE 


211 


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212  AGRICULTURAL  BACTERIOLOGY 

milk  with  bacteria  capable  of  fermenting  the  sugar,  and 
with  others  that  produce  propionic  acid  and  carbon-dioxide. 
The  milk  is  heated  to  about  135°  F.  and  the  curd  is  removed 
from  the  whey  in  one  mass,  so  as  not  to  allow  it  to  become 
cool,  which  checks  the  growth  of  Bad.  Bulgaricum  in  the 
curd. 

At  every  step  in  the  making  of  this  and  other  kinds  of 
cheese,  the  process  is  conducted  in  a  manner  that  influences 
the  growth  of  certain  groups  of  organisms.  Of  course, 
these  methods  were  primarily  worked  out  entirely  from  the 
standpoint  of  experience;  but  more  recently  their  relation 
to  the  action  of  certain  bacterial  groups  has  been  more 
definitely  traced. 

In  the  making  of  cheddar  cheese  the  salt  is  added  to  the 
finely  cut  curd  before  it  is  placed  in  the  press,  but  in  the 
case  of  Swiss  cheese  the  salt  is  applied  to  the  surface  of  the 
cheese.  The  most  marked  characteristic  of  Swiss  cheese  is 
the  presence  of  gas-holes,  ranging  from  the  size  of  a  cherry 
to  that  of  a  walnut,  which  are  scattered  quite  uniformly 
through  the  interior  of  the  cheese.  These  so  called  eyes 
are  formed  by  the  fermentation  of  the  lactates  with  the 
formation  of  propionic  acid  and  carbon-dioxide,  the  latter 
causing  the  holes  in  the  plastic  curd,  while  the  acid  influ- 
ences the  flavor  of  the  cheese.  These  organisms  can  not 
grow  in  the  presence  of  salt,  and  it  is  therefore  essential 
that  an  opportunity  first  be  given  for  their  growth.  Later 
the  application  of  salt  to  the  outside  checks  the  development 
of  these  gas- forming  organisms  as  the  salt  gi.*adually  pene- 
trates the  substance  of  the  cheese. 

Mold-ripened  cheese. — Roquefort,  a  French  cheese  made 
from  sheep's  milk,  Gorgonzola,  an  Italian  cheese,  and  Stil- 
ton cheese,  made  in  England,  are  illustrations  of  hard,  firm 
cheese  that  contain  molds.  Not  only  does  the  presence  of 
these  molds  confer  a  peculiar  flavor  and  appearance  on  the 


CHEESE  213 

cheese,  but  undoubtedly  the  ripening  or  digestive  changes 
are  influenced  by  these  types  of  organisms.  With  the 
Roquefort  type  a  green-spored  mold,  quite  similar  to  the 
ordinary  bread  mold,  is  grown  on  rye  bread,  which,  after 
drying,  is  powdered  and  the  powder  sprinkled  over  the 
curd  before  it  is  placed  in  the  press.  In  order  that  the 
mold  may  have  the  necessary  supply  of  air  for  the  matur- 
ing of  the  spores,  the  cheese  is  pierced  with  many  small 
holes.  The  green  color  of  the  mold  imparts  to  the  cheese 
a  marbled  appearance,  and  the  peculiar  flavor  is  due,  at 
least  in  part,  to  the  same  factor.  In  the  other  varieties 
mentioned,  the  mold  is  not  added  intentionally,  reliance 
being  placed  on  the  contamination  in  the  factory  during  the 
process  of  making. 

Soft  cheese. — In  the  making  of  Camembert,  a  French 
cheese,  the  curd  produced  by  rennet  is  not  cut,  but  is  placed 
in  small  molds  to  allow  the  whey  to  drain  off.  After  re- 
moval from  the  press  the  cheeses  are  placed  in  a  very  moist 
room.  The  lactic  fermentation  goes  on  rapidly  in  the 
cheese,  changing  the  curd  to  an  acid  mass  that  is  favorable 
for  the  growth  of  molds.  The  characteristic  mold  of  milk, 
O'idium  lactis,  and  a  white-spored  mold,  related  to  the  mold 
that  grows  in  Rociuefort  cheese,  are  essential  to  the  ripening 
and  the  development  of  the  characteristic  flavor.  It  is  es- 
sential that  a  certain  balance  be  maintained  between  the 
two  types  of  molds,  which  can  be  accomplished  only  by 
regulation  of  the  temperature  and  moisture  conditions 
within  certain  limits.  The  inability  of  the  maker  to  control 
these  conditions  makes  the  ripening  a  difficult  problem,  and 
a  large  portion  of  the  cheese  is  of  low  value  because  of  the 
non-development  of  the  typical  flavor. 

Brie,  Limburger,  and  brick  cheese  are  other  varieties  of 
soft  cheese  that  are  made  and  ripened  in  a  manner  similar 
to  Camembert. 


214  AGRICULTURAL  BACTERIOLOGY 

The  manufacture  of  cheese  is  an  industry  that  is  closely 
connected  with  the  farm,  and  is  an  example  of  the  value 
that  microorganisms  exert  in  the  preparation  of  a  valuable 
food  product.  It  indicates  how  valuable  the  products  of 
decomposition  may  be  in  imparting  a  desirable  flavor  to 
what  would  otherwise  be  a  tasteless  product. 


CHAPTER  XVIII 
THE  BACTERIOLOGICAL  CONTROL  OF  FOODS 

The  various  American  governmental  units,  national, 
State,  and  municipal,  are  all  expendinjj:  much  effort  in  at- 
tempting to  control  the  quality  of  food  supplies.  While 
national  activity  is  confined  to  foods  embraced  in  interstate 
commerce,  and  in  the  main  is  concerned  with  those  that 
are  preserved,  yet  the  interstate  control  of  fresh  meats  is 
a  large  factor  in  governmental  enterprise.  As  far  as  mu- 
nicipal control  is  concerned,  the  re2:ulatory  service  includes 
in  the  main  only  fresh  food  products,  and  of  these  milk  is 
of  the  most  importance.  With  the  recognition  of  the  fact 
that  milk  is  the  chief  food  product  in  its  relation  to  health, 
especially  of  children,  much  more  attention  has  been  given 
of  late  years  to  the  formulation  of  sanitary  rules  than  ever 
before.  Even  small  cities  and  towns  are  now  dealing  in  a 
direct  way  with  dairymen,  so  that  by  far  the  larger  part 
of  milk  supplies  used  for  direct  consumption  now  comes 
under  some  kind  of  supervision. 

In  order  to  have  the  milk  reach  the  consumer  in  the  city 
in  an  unchanged  condition,  the  greatest  care  must  be  ob- 
served by  all  who  handle  it.  The  regulations  that  a  mod- 
ern city  imposes  on  the  milk  dealer  and  on  the  producer 
are  complex  and  cover  every  phase  of  its  production  and 
handling  that  can  in  any  way  affect  the  value  of  the  milk 
as  human  food.  A  city  can  enforce  its  regulations  by  re- 
fusing to  allow  the  sale  of  milk  that  has  not  been  produced 
in  conformity  therewith.  In  order  to  determine  whether 
the  regulations  are  observed,  two  types  of  inspection  are 

215 


216  AGRICULTURAL  BACTERIOLOGY 

maintained:  first,  the  examination  of  the  milk  in  the  city 
as  to  the  number  and  kind  of  bacteria  it  contains ;  and,  sec- 
ond, an  inspection  of  the  dairy  farms  as  to  the  methods 
there  used  and  to  the  health  of  the  animals.  A  summary 
of  the  rules  imposed  by  the  city  of  New  York  follows.  It 
will  be  noted  that  the  rules  are  intended  to  force  the  pro- 
duction of  a  clean  and  healthful  milk. 

THE  cows 

1.  The  cows  must  be  kept  clean,  and  manure  must  not  be 
permitted  to  collect  upon  the  tail,  sides,  udder,  or  belly  of 
any  milch-cow. 

2.  The  cows  should  be  groomed  daily,  and  all  collections 
of  manure,  mud,  or  other  filth  must  not  be  allowed  to  re- 
main upon  their  flanks,  udders,  or  bellies  during  milking. 

3.  The  clipping  of  long  hairs  from  the  udder  and  flanks 
of  the  cows  is  of  assistance  in  preventing  the  collection  of 
filth  which  may  drop  into  the  milk.  The  hair  on  the  tails 
should  be  cut,  so  that  the  brush  will  be  well  above  the 
ground. 

4.  The  udders  and  teats  of  the  cow  should  be  thoroughly 
cleaned  before  milking ;  this  to  be  done  by  thorough  brush- 
ing and  the  use  of  a  cloth  and  warm  water. 

5.  To  prevent  the  cows  from  lying  down  and  getting 
dirty  between  cleaning  and  milking,  a  throat-latch  of  rope 
or  chain  should  be  fastened  across  the  stanchions  under  the 
cow 's  neck. 

6.  Only  feed  that  is  of  good  quality,  and  only  grain  and 
coarse  fodders  that  are  free  from  dirt  and  mold,  should 
be  used.  Distillery  waste  or  any  substance  in  a  state  of 
fermentation  or  putrefaction  must  not  be  fed. 

7.  Cows  that  are  not  in  good  flesh  and  condition  should 
be  immediately  removed  and  their  milk  kept  separate  until 
their  health  has  been  passed  upon  by  a  veterinarian. 


CONTROL  OF  FOODS  217 

8.  An  examination  by  a  veterinary  surgeon  should  be 
made  at  least  once  a  year. 

THE   STABLE 

9.  No  stagnant  water,  hog-pen,  privy,  or  uncovered  cess- 
pool or  manure  pit  should  be  maintained  within  one  hun- 
dred feet  of  the  cow  stable. 

10.  The  cow  stable  should  be  provided  with  some  ade- 
quate means  of  ventilation,  either  by  the  construction  of 
sufficient  air-chutes  extending  from  the  room  in  which  the 
cows  are  kept  to  the  outside  air,  or  by  the  installation  of 
muslin  stretched  over  the  window  openings. 

11.  Windows  should  be  installed  in  the  cow  barn  to  pro- 
vide sufficient  light  (2  square  feet  of  window  light  to  each 
600  cubic  feet  of  air  space  the  minimum)  and  the  window- 
panes  be  washed  and  kept  clean. 

12.  There  should  be  at  least  600  cubic  feet  of  air  space 
for  each  cow. 

13.  Milch-cows  should  be  kept  in  a  place  that  is  used  for 
no  other  purpose. 

14.  Stable  floors  should  be  made  water-tight,  be  properly 
graded  and  well  drained,  and  be  of  some  non-absorbent  ma- 
terial. Cement  or  brick  floors  are  the  best,  as  they  can  be 
more  easily  kept  clean  than  those  of  wood  or  earth. 

15.  The  feeding-troughs  and  platforms  should  be  well 
lighted  and  kept  clean  at  all  times. 

16.  The  ceiling  should  be  thoroughly  swept  down  and 
kept  free  from  hanging  straw,  dirt,  and  co])webs. 

17.  The  ceiling  must  be  so  constructed  that  dust  and  dirt 
therefrom  shall  not  readily  fall  to  the  floor  or  into  the  milk. 
If  the  space  over  the  cows  is  used  for  the  storage  of  hay, 
the  ceiling  should  be  made  tight  to  prevent  chaff  and  dust 
from  falling  through. 

18.  The  walls  and  ledges  should  be  thoroughly  swept 


218  AGRICULTURAL  BACTERIOLOGY 

down  and  kept  free  from  dust,  dirt,  manure,  or  cobwebs, 
and  the  floors  and  premises  be  kept  free  from  dirt,  rubbish, 
and  decaying  animal  or  vegetable  matter  at  all  times. 

19.  The  cow  beds  should  be  so  graded  and  kept  that  they 
will  be  clean  and  sanitary  at  all  times. 

20.  Stables  should  be  whitewashed  at  least  twice  a  year, 
unless  the  walls  are  painted  or  are  of  smooth  cement. 

21.  Manure  must  be  removed  from  the  stalls  and  gutters 
at  least  twice  daily.  This  must  not  be  done  during  milk- 
ing, nor  within  one  hour  prior  thereto. 

22.  Mianure  should  be  taken  from  the  barn,  preferably 
drawn  to  the  field.  When  the  weather  is  such  that  this  can 
not  be  done,  it  should  be  stored  not  nearer  than  200  feet 
from  the  stable,  and  the  manure  pile  should  be  so  located 
that  the  cows  can  not  get  at  it. 

23.  The  liquid  matter  should  be  absorbed  and  removed 
daily,  and  at  no  time  be  allowed  to  overflow  or  saturate  the 
ground  under  or  around  the  cow  barn. 

24.  Manure  gutters  should  be  from  six  to  eight  inches 
deep,  and  constructed  of  concrete,  stone,  or  some  non- 
absorbent  material. 

25.  The  use  of  land  plaster  or  lime  is  recommended  upon 
the  floors  and  gutters. 

26.  Only  bedding  that  is  clean,  dry,  and  absorbent 
should  be  used,  preferably  sawdust,  shavings,  dried  leaves, 
or  straw.     No  horse  manure  should  be  used  as  bedding. 

27.  The  flooring  where  the  cows  stand  should  be  so  con- 
structed that  all  manure  will  drop  into  the  gutter  and  not 
upon  the  floor  itself. 

28.  The  floor  should  be  swept  daily.  This  must  not  be 
done  within  one  hour  prior  to  milking-time. 

29.  If  individual  drinking  basins  are  used  for  the  cows, 
they  should  be  frequently  drained  and  cleaned. 

e30.  All  live  stock  other  than  cows  should  be  excluded 


CONTROL  OF  FOODS  219 

from  the  room  in  which  the  milch-cows  are  kept.  (Calf  or 
bull  pens  may  be  allowed  in  the  same  room  if  kept  in  the 
same  clean  and  sanitary  manner  as  the  cow  beds.) 

31.  The  barnyard  should  be  well  drained  and  dry,  and 
should  be  sheltered  as  much  as  possible  from  the  wind  and 
cold.     Manure  should  not  be  allowed  to  collect  therein. 

32.  A  suitable  place  in  some  separate  building  should  be 
provided  for  the  use  of  the  cows  when  sick,  and  separate 
quarters  must  be  provided  for  the  cows  when  calving. 

33.  There  should  be  no  direct  opening  from  any  silo  or 
grain  pit  into  the  room  in  which  the  milch-cows  are  kept. 

THE   MILK-HOUSE 

34.  A  milk-house  miist  be  provided  which  is  separated 
from  the  stable  and  dwelling.  It  should  be  located  on  ele- 
vated ground,  with  no  hog-pen,  privy,  or  manure  pile  within 
100  feet. 

35.  It  must  be  kept  clean,  and  not  used  for  any  purpose 
except  the  handling  of  milk. 

36.  The  milk-house  should  be  provided  with  sufficient 
light  and  ventilation,  with  floors  properly  graded  and  made 
water-tight. 

37.  It  should  be  provided  with  adjustable  sashes  to  fur- 
nish sufficient  light,  and  some  proper  method  of  ventilation 
should  be  installed. 

38.  The  milk-house  should  be  provided  with  an  ample 
supply  of  clean  water  for  cooling  the  milk,  and  if  it  is  not 
a  running  supply,  the  water  should  be  changed  twice  daily. 
Also  a  supply  of  clean  ice  should  be  provided  to  be  used  for 
cooling  the  milk  to  50°  F.  within  two  hours  after  milking. 

39.  Suitable  means  should  be  provided  within  the  milk- 
house  to  expose  the  milk-pails,  cans,  and  utensils  to  the  sun 
or  to  live  steam. 

40.  Facilities  consisting  of  wash-basins,  soap,  and  towel 


220  AGRICULTURAL  BACTERIOLOGY 

should  be  provided  for  the  use  of  milkers  before  and  during 
milking.  In  the  summer  months  the  milk-house  should  be 
properly  screened  to  exclude  flies, 

THE   MILKERS   AND    MILKING 

41.  Any  person  having  any  communicable  or  infectious 
disease,  or  one  caring  for  persons  having  such  disease,  must 
not  be  allowed  to  handle  the  milk  or  milk  utensils. 

42.  The  hands  of  the  milkers  must  be  thoroughly  washed 
with  soap  and  water,  and  carefully  dried  on  a  clean  towel, 
before  milking. 

43.  Clean  overalls  and  jumpers  should  be  worn  during 
the  milking  of  the  cows.  They  should  be  used  for  no  other 
purpose,  and  when  not  in  use  should  be  kept  in  a  clean 
place  protected  from  dust. 

44.  The  milker's  hands  and  the  teats  of  the  cow  should 
be  kept  dry  during  milking.  The  practice  of  moistening 
the  hands  with  milk  is  to  be  condemned. 

45.  The  milking-stools  should  be  at  all  times  kept  clean. 
Iron  stools  are  recommended. 

46.  The  first  streams  from  each  teat  should  be  rejected, 
as  this  foremilk  contains  more  bacteria  than  the  rest  of  the 
milk. 

47.  All  milk  drawn  from  the  cows  fifteen  days  before  or 
five  days  after  parturition  should  be  rejected. 

48.  The  pails  in  which  the  milk  is  drawn  should  have  as 
small  an  opening  at  the  top  as  can  be  used  in  milking,  the 
top  opening  preferably  not  to  exceed  eight  inches  in  diame- 
ter. This  lessens  the  contamination  by  dust  and  dirt  dur- 
ing milking. 

49.  The  milking  should  be  done  rapidly  and  quietly,  and 
the  cows  should  be  treated  kindly. 

50.  Dry  fodder  should  not  be  fed  to  the  cows  during  or 


CONTROL  OF  FOODS  221 

just  before  milking,  as  dust  therefrom  may  fall  into  the 
milk. 

51.  All  milk  utensils,  including  pails,  cans,  strainers,  and 
dippers,  must  be  kept  thoroughly  clean,  and  must  be  washed 
and  scalded  after  each  using ;  and  all  seams  in  these  utensils 
should  be  cleaned,  scraped,  and  soldered  flush. 

THE  MILK 

52.  Milk  from  diseased  cows  must  not  be  shipped. 

53.  The  milk  must  not  be  in  any  way  adulterated. 

54.  The  milk  as  soon  as  drawn  should  be  removed  to  the 
milk-house  and  immediately  strained  and  cooled  to  the 
proper  temperature. 

55.  All  milk  must  be  cooled  to  a  temperature  below  50°  F. 
within  two  hours  after  being  drawn,  and  kept  thereafter 
below  that  until  delivered  to  the  creamery. 

56.  The  milk  should  be  strained  into  cans  that  are  stand- 
ing in  ice  water  which  reaches  the  neck  of  the  can.  The 
more  rapidly  the  milk  is  cooled,  the  safer  it  is  and  the  longer 
it  will  keep  sweet.  Ice  should  be  used  in  cooling  milk,  as 
very  few  springs  are  cold  enough  for  the  purpose. 

57.  If  separators  are  used,  they  should  stand  where  the 
air  is  free  from  dust  or  odors,  and  on  no  account  should 
they  be  used  in  the  stable  or  out  of  doors. 

58.  Milk-strainers  should  be  kept  clean,  scalded  a  second 
time  just  before  using,  and  if  cloth  strainers  are  used,  sev- 
eral of  them  should  be  provided,  in  order  that  they  may  be 
chaiged  frequently  during  the  straining  of  the  milk. 

59.  The  use  of  any  preservative  or  coloring  matter  is 
adulteration,  and  its  use  by  a  producer  or  shipper  will  be 
a  sufficient  cause  for  the  exclusion  of  his  product  from  the 
city  of  New  York. 


222  AGRICULTURAL  BACTERIOLOGY 


WATER    SUPPLY 

60.  The  water  supply  used  in  the  dairy  and  for  washing 
utensils  should  be  absolutely  free  from  any  contamination, 
sufficiently  abundant  for  all  purposes,  and  easy  of  access. 

61.  This  supply  should  be  protected  against  flood  or  sur- 
face drainage. 

62.  The  privy  should  be  located  not  nearer  than  100  feet 
of  the  source  of  the  water  supply,  or  else  be  provided  with 
a  water-tight  box  that  can  be  readily  removed  and  cleaned, 
and  so  constructed  that  at  no  time  will  the  contents  over- 
flow or  saturate  the  surrounding  ground. 

63.  The  source  of  the  water  supply  should  be  rendered 
safe  against  contamination  by  having  no  stable,  barnyard, 
pile  of  manure,  or  other  source  of  contamination  located 
within  200  feet  of  it. 

In  order  that  the  farm  inspection  will  be  as  effective  as 
possible,  and  to  make  the  work  of  the  several  inspectors  as 
uniform  as  may  be,  the  dairies  are  scored.  A  copy  of  the 
score-card  follows. 

DEPARTMENT  OF  HEALTH 

The  City  of  New  York 

Division  of  General 

Sanitary  Inspecton  Dairy  Report 

Inspection  No Time A.  P.  M.     Date 192.  . 

1     Dairyman    Owner 


2  P.  0.  Address  P.  0.  Address. .. State. 

3  County State Party  Interviewed 


4  Milk  delivered  to  Creamery  at Formerly  at 

5  Operated   by    Address 

6  Distance  of  farm  from  Creamery Occupied  farm  since. .  .  . 

7  No.  Cows No.  Milking No.  Qts.  Produced 

8  All  persons  in  the  households  of  those  engaged  in  producing  or 

handling    milk    are free    from    all    infectious    disease. 

Weekly   reports   are being   filed 

9  Date  and  nature  of  last  case  on  farm 

10     WATER  SUPPLY  for  utensils  is  from  a located 


CONTROL  OF  FOODS 


223 


feet  deep  and  apparently  is pure  and 

wholesome State  any  possible  contamination  lo- 
cated within  200  feet  of  source  of  water  supply  or  if  water  sup- 
ply is  not  protected  against  surface  drainage 


.192..     Result 

.ft.     Width ft. 


11  Water  supply  on  this  farm  analyzed. 

12  Style  of  Cow   Barn Length... 

TltML'lit  of  ceiling ft. 

13  Dairy  Rules  of  the  Department  of  Health  are posted 


Dairy  Herd  examined  by on 

Report 


192. 


EQUIPMENT 


Perfect    Allow 


15  COW   STABLE   is located   on   elevated 

ground  with  no  stagnant  water,  hog-pen, 
privy,  uncovered  cesspool,  or  manure  pit 
within  100  feet   

16  FLOORS,  other  than  cow  beds,  are 

of  concrete  or  some  non-absorbent  material. .  . 

17  Floors  are properly  graded  and  water- 

tight     

18  Cow  beds  are of  concrete  or  planks  laid  on 

concrete     

19  DROPS  are.  .  .  .constructed  of  concrete,  stone,  or 

some  non-absorbent  material   .  .  .  .* 

20  Drops  are water-tight  and  space  beneath 

is  clean  and  dry 

21  CEILING  is  constructed  of and  is 

tight    and    dust-proof 

22  WINDOWS    No total    square    feet 

there  is 2  square  feet  of  window 

light  for  ea(h  600  cu.  ft.  air  space  (1  sq.  ft. 
per  each  000  cu.  ft  — 1 ) 

23  VENTILATION   consists   of sq.   ft.   muslin 

covered   openings  or sq.   ft.  open   chutes 

in    ceiling   or which    is    sufficient 

3,  fair  2,  poor  1,  insufficient  0 

24  AIR  SPACE  is cu.  ft.  per  cow   (600  and 

over— 3)  (500  to  600—2)  (400  to  500—1) 
(under   400—0)     

25  LIVE   STOCK,  other  than  cows,  are ex- 


224 


AGRICULTURAL  BACTERIOLOGY 


Perfect    All 


26 


27 


28 


29 


30 


31 


32 


33 


34 


35 


36 


38 


"EOLUlVMEliT— Continued 
eluded   from   rooms   in   which   milch-cows  are 
kept    

There  is direct  opening  from  stable 

into  silo  or  grain  pit 

Separate  quarters  are provided  for 

cows  when  calving  or  sick 

COW-YARD  is properly  graded  and 

drained    

WATER    SUPPLY   for   cows   is unpol- 
luted and   plentiful    

MILK-HOUSE    has direct   opening   into 

cow-barn  or  other  building 

Milk-house  has sufficient  light  and  ventila- 
tion     

Floor  is properly  graded  and  water- 
tight     

Milk-house  is properly  screened  to  ex- 
clude flies   

MILK  PAILS  are of  smoothly  tinned 

metal  in  good  repair  

Milk-pails  have all  seams  soldered 

flush     

Milk-pails   are of   the  small-mouthed 

design,  top  opening  not  exceeding  8  inches  in 
diameter.     Diameter     

Racks    are provided   to   hold   milk-pails 

and  cans  when  not  in  use 

Special  milking   suits  are provided 


40 


METHODS 

39  STABLE    INTERIOR    painted    or    whitewashed 

on which  is  satisfactory  3,  fair  2, 

unsatisfactory  1,  never  0 

40  FEEDING-TROUGHS,    platforms,    or    cribs    are 

well  lighted  and   clean 

41  Ceiling    is free   from   hanging    straw, 

dirt,  or  cobwebs    

42  Window-panes  are washed  and  kept 

clean    


CONTROL  OF  FOODS 


225 


Perfect    Allow 


43 


44 


45 


40 


47 

48 
49 

50 

51 

52 

53 

54 


55 


56 

57 

58 
59 

60 

61 


62 
63 


METHODS — Continued 

WALLS  AND  LEDGES  are free  from 

(lilt,  (lust,  inamirc,  or  coliwebs 

FLOORS  AND  PREMISES  are free  from 

dirt,  rubbish  or  decayed  animal  or  vegetable 

matter 

COW  BEDS  are clean,  dry,  and  no  horse 

manure^  used  thereon   

Manure  is removed  to  field  daily  4, 

to  at  least   100  feet  from  l)arn  2,  stored  less 
than  100  feet  or  where  cows  can  get  at  it  0. , 

Liquid  Matter  is allowed  to  saturate 

j^round  under  or  around  cow-barn 

Milking-stools    are clean 

Cow-yard  is clean  and  free  from 

manure    

COWS  have been  tuberculin  tested  and 

all  tuberculous  cows  remove<l 

Cows  are all  in  good  flesh  and  condi- 
tion at  time  of  inspection 

Cowa  are all  free  from  clinging  ma- 
nure and  dirt,      (No  dirty) 

LONG  HAIRS  are kept  short  on  belly, 

Hanks,   udder,  and   tail 

UDDER   AND  TEATS   of  cow  are 

thoron<;hly   brushed  and  wiped   with   a  clean 

damp  cloth  before  milking 

ALL  FEED  is of  good  quality  and  distil- 
lery   waste   or   any    substance    in   a   starte    of 

putrefaction     is fed 

MILKING  is done  with  dry  hands 

FORE  MILK  or  first  few  streams  from  each  teat 

is discardetl     

Clothing  of   milkers   is clean 

Facilities  for  washing  hands  of  milkers  are. .  . . 

provided  in  cow-barn  ot  milk-house 

Milk    is    strained    at and in 

clean   atmosphere    

Milk  is cooled  within  two  hours  after 

milking  to  50  degrees  F.  3,  to  55  degrees  F.  2, 

to  60  degrees  F,  1 

Tee  is used  for  cooling  milk 

MILK-HOUSE   is free   from  dirt,   rub- 


226 


AGRICULTURAL  BACTERIOLOGY 


bish,  and  all  material  not  used  in  the  handling 
and   storing  of  milk 

64  Milk   Utensils    are rinsed    with    cold 

water    immediately    after    using    and    washed 
clean  with  hot  water  and  washing  solution .  .  . 

65  Utensils  are sterilized  by  steam  or 

boiling  water  after  each  using 

66  Privy  is in  sanitary  condition,  with 

vault  and  seats covered  and  pro- 
tected      


Remarks 


Equipment  40   per   cent.     Score per  cent. 

Methods   60   per   cent.     Score per  cent. 

Perfect  Dairy   100  per  cent.     Score per  cent. 

A  copy  of  the  completed  report  is  left  with  the  dairyman. 

It  is  to  be  noted  that,  almost  without  exception,  each  of 
the  foregoing  rules  has  a  direct  effect  in  preventing  the 
contamination  of  the  milk  with  bacteria  that  injure  its 
keeping  quality,  its  taste  and  odor,  or  its  healthfulness.  A 
rigid  adherence  to  the  rules  will  insure  the  production  of 
milk  of  high  quality.  The  task  of  the  inspector  is  to  de- 
termine which  producers  are  derelict  in  their  methods,  and 
then  to  aid  them  in  improving  their  methods  and  equip- 
ment. It  should  be  remembered  that  methods  are  of  far 
greater  importance  in  the  production  of  good  milk  than 
equipment.  Additional  care  may  make  up  for  the  lack  of 
suitable  stables  and  utensils,  but  -the  most  elaborate  equip- 
ment is  of  no  value  unless  supplemented  by  good  methods. 

It  is  also  to  be  noted  that  the  conditions  outlined  in  the 
rules  are  nothing  more  than  those  any  milk  producer  should 
be  willing  to  establish  of  his  own  volition.  Some  may  have 
but  little  influence  on  the  quality  of  the  milk  produced,  but 


CONTROL  OF  FOODS  227 

are  nevertheless  to  be  classed  as  essential  conditions  in  a 
plant  producing  human  food.  The  dairy  farm  is  a  manu- 
facturing plant,  where  vegetable  matter,  not  available  for 
human  food,  is  changed  by  the  dairy  cow  to  the  most  valu- 
able human  food.  The  most  important  factor  in  the  pro- 
duction of  good  milk  is  the  dairyman  and  his  conception  of 
his  duty  to  the  people  consuming  his  milk. 

Before  the  farm  inspection  is  carried  out  the  creameries 
to  which  the  milk  is  delivered  by  the  farmers  are  inspected 
at  the  time  the  milk  is  being  delivered.  The  temperature 
of  the  milk  and  its  cleanliness  ^re  noted.  In  the  creamery 
the  straining,  cooling,  and  handling  of  the  milk  are  ob- 
served, as  well  as  the  washing  of  the  milk-cans  and  other 
utensils,  the  construction  and  condition  of  the  creamery, 
the  opportunity  for  the  water  supply  to  become  contami- 
nated, and  the  presence  of  infectious  diseases  among  the 
employes. 

Grades  of  milk. — It  has  come  to  be  recognized  that  milk 
varies  in  its  quality,  which  is  a  complex  property  depending 
on  many  factors.  It  is  recognized  that  it  costs  more  to  pro- 
duce good  milk  than  poor  milk,  and  that  the  former  is  of 
more  value  to  the  consumer.  The  grading  of  milk  has, 
therefore,  been  introduced,  so  that  the  consumer  may  know 
something  of  the  quality  of  the  milk  he  purchases.  The 
following  are  the  grades  established  by  the  State  of  New 
York: 

All  milk  sold  and  ofTered  for  sale  at  retail,  except  milk  sold  ob 
offered  for  sale  as  sour  milk  under-  its  various  designations,  shall 
bear  one  of  the  designations  provided  in  this  regulation,  which  con- 
stitute the  minimum  requirements  permitted  in  this  State. 

Xo  term  shall  be  used  to  designate  the  grade  or  quality  of  milk  or 
cream  which  is  sold  or  offered  for  sale,  except: 

"Certified" 

"Grade  A  raw" 

"Grade  A  pasteurized" 

"Grade  B  raw" 


228  AGRICULTURAL  BACTERIOLOGY 

"Grade  B  pasteurized" 
"Grade  C  raw" 
"Grade  C  pasteurized" 

Certified. — No  milk  or  cream  shall  be  sold  or  offered  for  sale  as 
"Certified"  unless  it  conforms  to  the  following  requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  officer. 

All  cows  producing  such  milk  or  cream  must  have  been  tested  at 
least  once  during  the  previous  year  with  tuberculin,  and  any  cow 
reacting  thereto  must  have  been  promptly  excluded  from  the  herd. 
The  reports  of  such  tuberculin  tests  must  be  filed  with  the  local 
health  ofiicer  and  the  milk  commission  of  the  county  medical  society 
in  the  municipality  and  county  respectively  in  which  such  milk  is 
delivered  to  the  consumer. 

Such  milk  must  not  at  any  time  previous  to  delivery  to  the  con- 
sumer contain  more  than  10,000  bacteria  per  cubic  centimeter,  and 
such  cream  not  more  than  50,000  bacteria  per  cubic  centimeter. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-card  prescribed  by  the  State  Commissioner  of 
Health,  not  less  than  35  per  cent,  for  equipment  and  not  less  than 
55  per  cent,  for  methods. 

Such  milk  and  cream  must  be  delivered  within  thirty-six  hours  of 
the  time  of  milking. 

Such  milk  and  cream  must  be  delivered  to  consumers  only  in  con- 
tainers filled  at  the  dairy  or  central  bottling  plant. 

The  caps  must  contain  the  word  "Certified"  and  bear  the  certifica- 
tion of  a  milk  commission  appointed  by  the  county  medical  society 
organized  under  and  chartered  by  the  medical  society  of  the  State 
of  New  York,  and  must  also  contain  the  name  and  address  of  the 
dairy  as  well  as  the  date  of  milking. 

Every  employee  before  entering  upon  the  performance  of  his  duties 
shall  be  examined  by  a  duly  licensed  physician,  and  the  reports  of 
such  examination  shall  be  sent  to  the  milk  commission  certifying  the 
railk  from  such  dairy. 

The  milkers  and  all  persons  handling  tlfe  milk  must  be  provided 
with  suits  and  caps  of  washable  material  which  shall  be  worn  while 
milking  or  handling  the  milk  and  shall  not  be  worn  at  other  times. 
When  not  in  use  these  garments  must  be  kept  in  a  clean  place  free 
from  dust.  Not  less  than  two  clean  suits  and  caps  must  be  furnished 
weekly.  The  hands  of  the  milkers  must  be  washed  with  soap  and 
hot  water,  and  well  dried  with  a  clean  towel,  before  milking. 

Grade  A  raw. — No  milk  or  cream  shall  be  sold  or  offered  for  sale 
as  "Grade  A  raw"  unless  it  conforms  to  the  following  requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  officer. 


CONTROL  OF  FOODS  220 

All  cows  producing  such  milk  or  cream  must  have  been  tested  at 
least  once  during  the  previous  year  with  tuln'rculin,  and  any  cow 
reacting  thereto  must  have  been  promptly  exclude<l  from  the  herd. 

Such  milk  must  not  at  anj-^  time  previous  to  delivery  to  the  con- 
sumer contain  more  than  60,000  bacteria  per  cubic  centimeter,  and 
such  cream  not  more  than  300,000  bacteria  per  cubic  centimeter. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-card  prescribed  by  the  State  Commissioner  of 
Health  not  less  than  25  per  cent,  for  equipment,  and  not  less  than 
50  per  cent,  for  methods. 

Such  milk  and  cream  must  be  delivered  within  tliirty-six  hours 
from  the  time  of  milking,  unless  a  shorter  time  shall  be  prescribed 
by  the  local  health  authorities. 

Such  milk  and  cream  must  be  delivered  to  consumers  only  in  con- 
tainers sealed  at  the  dairy  or  a  bottling  plant.  The  caps  or  tags 
must  be  white  and  contain  the  term  "Grade  A  raw"  in  large  black 
type,  and  tlie  name  and  address  of  the  dealer. 

Grade  A  pasteurized. — No  milk  or  cream  shall  be  sold  or  offered 
for  sale  as  "Grade  A  pasteurized"  unless  it  conforms  to  the  follow- 
ing rev^uirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  oflicer. 

All  cows  producing  »uch  milk  or  cream  must  be  healthy  as  dis- 
close<l  by  an  arnnual  physical  examination. 

Such  milk  or  cream  before  pasteurization  rtiust  not  contain  more 
than  200,000  Ijacteria  per  cubic  centimeter. 

Such  milk  must  not  at  any  time  after  pasteurization  and  pre- 
vious to  delivery  to  the  consumer  contain  more  than  30,000  bacteria 
per  cubic  centimeter,  and  such  cream  not  more  than  150,000  bac- 
teria per  cubic  centimeter. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-card  prescrilied  bj'  the  State  Commissioner  of 
Health  not  less  than  25  per  cent,  for  equipment  and  not  less  than 
43  per  cent,  for  methods. 

Such  milk  and  cream  must  be  delivered  within  thirty-six  hours 
after  pasteurization,  unless  a  shorter  time  shall  be  prescribed  by 
the  local  authorities. 

Such  milk  and  cream  must  be  delivered  to  consumers  only  in  con- 
t^ainer3  sealed  at  the  dairy  or  at  a  bottling  plant.  The  caps  or  tags 
must  l)e  white  and  contain  the  term  "Grade  A  pasteurized"  in  large 
black  type. 

Grade  B  raw. — Xo  milk  or  cream  shall  be  sold  or  offered  for  sale 
as  "Grade  B  raw"  unless  it  conforms  to  the  following  requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  officer. 


230  AGRICULTURAL  BACTERIOLOGY 

All  cows  producing  tiuch  milk  or  cream  must  be  healthy  as  dis- 
closed by  an  annual  pliysical  examination. 

Such  milk  must  not  at  any  time  previous  to  delivery  to  the  cus- 
tomer contain  more  than  200,000  Ijacteria  per  cubic  centimeter,  and 
such  cream  not  more  than  750,000  bacteria  per  cubic  centimeter. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-cards  prescribed  by  the  State  Commissioner  of 
Health  not  less  than  23  per  cent,  for  equipment  and  not  less  than 
37  per  cent,  for  methods. 

Such  milk  and  cream  must  be  delivered  within  thirty-six  hours 
from  the  time  of  milking,  unless  a  shorter  time  shall  be  prescribed 
by  the  local  health  authorities. 

The  caps  or  tags  on  the  containers  must  be  white  and  contain  the 
term  "Grade  B  raw"  in  large,  bright  green  type,  and  the  name  of  the 
dealer. 

Grade  B  pasteurized. — No  milk  or  cream  shall  be  sold  or  offered 
for  sale  as  "Grade  B  pasteurized"  unless  it  conforms  to  the  following 
requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  officer. 

All  cows  producing  such  milk  or  cream  must  be  healthy  as  dis- 
closed by  an  annual  physical  examination. 

Such  milk  or  cream  before  pasteurization  must  not  contain  more 
than  1,500,000  bacteria  per  cubic  centimeter. 

Such  milk  must  not  at  any  time  after  pasteurization  and  previous 
to  delivery  to  the  consumer  contain  more  than  100,000  bacteria  per 
cubic  centimeter,  and  such  cream  not  more  than  500,000  bacteria 
per  cubic  centimeter. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-card  prescribed  by  the  State  Commissioner  of 
Health  not  less  than  20  per  cent,  for  e(iuipment  and  not  less  than 
35  per  cent,  for  methods. 

Such  milk  must  be  delivered  W'ithin  thirty-six  hours  after  pas- 
teurization between  April  1  and  November  1  and  within  forty-eight 
hours  after  pasteurization  between  November  1  and  April  I,  and 
such  cream  within  forty-eight  hours  after  pasteurization,  unless  a 
shorter  time  is  prescribed  by  the  local  health  authorities. 

The  caps  or  tags  on  the  containers  must  be  white  and  contain  the 
term  "Grade  B  pasteurized"  in  large,  bright  green  type,  and  the 
name  of  the  dealer. 

Grade  C  raw. — No  milk  or  cream  shall  be  sold  or  offered  for  sale 
as  "Grade  C  raw"  unless  it  conforms  to  the  following  requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold 
a  permit  from  the  local  health  officer. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 


CONTROL  OF  FOODS  231 

scored  on  the  score-card  prescribed  by  the  State  Commissioner  of 
Health  not  less  than  40  per  cent. 

Such  milk  and  cream  must  be  delivered  within  forty-eight  hours 
from  the  time  of  milkinir,  unless  a  shorter  time  shall  be  prescribed 
by  the  local  health  authorities. 

The  caps  or  tags  affixed  to  the  containers  must  be  white  and  con- 
tain the  term  "(Irade  C  raw"  in  large  red  type. 

Grade  C  pasteurized. — Xo  milk  or  cream  shall  be  sold  or  offered 
for  sale  as  '(irade  C  pasteuri/ed"  unless  it  conforms  to  the  following 
requirements: 

The  dealer  selling  or  delivering  such  milk  or  cream  must  hold  a 
permit  from  the  local  health  oflicer. 

Such  milk  and  cream  must  be  produced  on  farms  which  are  duly 
scored  on  the  score-card  prescribed  by  the  State  Commissioner  of 
Health  not  less  than  40  per  cent. 

Such  milk  and  cream  must  be  delivered  within  forty-eight  hours 
after  pasteurization,  unless  a  shorter  time  shall  l>e  prescribed  by  the 
local  health  authorities. 

'J'lic  caps  or  tags  allixed  to  the  containers  must  be  white  and  con- 
tain the  term  "(irade  C  pasteuri/ed"  in  large  red  type. 

It  is  to  be  noted  that  the  grades  of  milk  are  based  on  the 
bacterial  content  of  the  milk  and  on  the  opportunity  for 
the  milk  to  become  contaminated  with  pathogenic  organ- 
isms. From  the  statements  made  in  a  previous  chapter,  it 
is  evident  that  the  number  of  bacteria  in  any  sample  of 
milk  is  dependent  upon  the  original  amount  of  contamina-. 
tion  and  the  extent  to  which  the  introduced  bacteria  have 
grown.  The  latter  is  dependent  on  the  age  of  the  milk  and 
the  temperature  at  which  it  has  been  held.  A  high  bac- 
terial content  is  indicative  of  poor  milk,  while  a  low  bac- 
terial content  can  be  obtained,  in  the  case  of  raw  milk,  only 
where  due  attention  is  paid  to  cleanliness  and  cooling. 

This  relation  between  the  quality  of  milk  and  its  bacterial 
content  has  led  many  cities  to  adopt  numerical  bacterial 
standards,  even  when  grades  of  milk  have  not  been  estab- 
lished. Boston  requires  that  the  milk  shall  not  contaifi 
more  than  500,000  bacteria  per  cubic  centimeter;  Rochester, 
New  York,  has  a  standard  of  100,000  per  cubic  centimeter; 


232  ACailCULTURAL  BACTERIOLOGY 

while  Chicao^o  requires  that  the  milk  on  arrival  in  the  city 
shall  contain  not  more  than  1,00(),()00  per  cubic  centimeter 
from  ^lay  first  to  September  thirtieth,  and  not  more  than 
500,000  between  October  1  and  April  30.  The  sale  of  milk 
containing  more  than  3,000,000  bacteria  per  cubic  centi- 
meter is  prohibited. 

It  has  been  urged  that  bacterial  standards  are  not  of 
value  since  the  healthfulness  of  milk  depends  on  the  kind 
of  bacteria  present  rather  than  on  the  number.  It  is  well 
recognized  that  milk  containing  millions  of  acid-forming 
organisms,  buttermilk,  is  a  healthful  food,  while  that  con- 
taining many  less  fcacteria  may  harbor  some  disease-produc- 
ing organisms.  It  has  been  urged  that  a  ([ualitative  stand- 
ard should  supplant  the  quantitative.  The  consumer  de- 
sires milk  that  has  been  produced  under  clean  conditions 
and  which  has  good  keeping  qualities.  The  harmless  forms 
of  bacteria  exert  the  greatest  influence  on  the  keeping  qual- 
ity. Experience  has  shown  that  the  quantitative  examina- 
tion of  the  milk  supply  as  it  comes  from  the  farm  is  the 
most  feasible  method  of  determining,  in  the  laboratory, 
whether  the  farmer  has  obeyed  the  rules  with  reference  to 
cleanliness  and  cooling  of  the  milk.  The  bacteriological  ex- 
amination also  gives  an  indication  as  to  whether  the  large 
number  of  bacteria  is  due  to  gross  contamination  of  the 
milk  with  mud  and  manure,  or  actual  growth  of  bacteria,  as 
in  old  milk.  In  the  latter  case  the  ordinary  acid-forming 
bacteria  will  usually  predominate  in  the  milk,  while  in  the 
former  the  number  of  kinds  of  bacteria  and  the  proportion 
between  the  kinds  will  be  changed.  It  is,  of  course,  evi- 
dent that  the  quantitative  standards  should  be  applied 
with  judgment. 

It  is  also  claimed  that  the  delay  in  securing  the  results 
in  the  quantitative  examination  of  milk  is  an  objection  to 
the  bacterial  standard,  since  the  milk  is  consumed  before 


CONTROL  OF  FOODS  233 

the  laboratory  findings  can  he  obtained.  It  is  true  that  it 
does  not  protect  the  community  as  far  as  the  particular  sam- 
ple is  concerned,  but  it  is  also  true  that  the  examination  is 
not  made  for  the  purpose  of  determining  the  condition  of 
the  particular  sample,  but  rather  to  determine  the  methods 
that  are  employed  on  any  particular  farm.  These  do  not 
vary  widely  from  day  to  day.  Thus  if  the  bacterial  con- 
tent of  a  number  of  samples  from  a  particular  source  is  uni- 
formly hijrh,  it  is  evident  that  conditions  surrounding  pro- 
duction need  investigation. 

If  the  milk  is  well  cooled  on  the  farm,  and  kept  cold  while 
being  shipped,  the  growth  of  bacteria  will  be  slow,  and  the 
condition  of  the  milk,  as  far  as  keeping  quality  is  con- 
cerned, much  better  than  if  less  care  is  used.  Some  cities 
have  temperature  standards;  New  York  requires  that  the 
milk  shall  be  cooled  to  50°  F.  on  the  farm,  and  shall  not  be 
above  50°  F.  on  arrival  in  the  city.  Others  require  that  it 
shall  not  be  above  50°  F.  on  delivery  to  the  consumer. 

Certified  milk. — In  many  cities  the  medical  societies  have 
appointed  milk  commissions,  which  adopt  rules  and  regula- 
tions concerning  the  production  of  milk  that  shall  receive 
the  certificate  of  the  commission.  Producers  who  desire  to 
have  their  milk  thus  certified  must  satisfy  the  commission 
that  they  are  able  to  conform  to  the  rules.  The  commission 
appoints  a  physician  to  examine  the  personnel  of  Ijie  farm, 
a  veterinarian  to  make  frequent  examinations  of  the  herd, 
a  chemist  to  examine  the  milk  as  to  its  content  in  fat  and 
other  solids,  and  a  bacteriologist  to  determine  the  bacterial 
content  of  the  milk.  The  rules  are  very  stringent,  and 
cover  every  point  that  may  in  any  way  influence  the  value 
of  the  milk  as  human  food.  In  order  to  conform  to  these 
requirements,  a  heavy  expenditure  must  be  incurred,  and 
the  business  must  pay  for  such  expert  service — hence  certi- 
fied milk  must  be  sold  at  high  prices.     This  price  makes  it 


234  AGRICULTURAL  BACTERIOLOGY 

a  special  product,  and  its  use  is  confined  mainly  to  infant 
feeding. 

The  bacterial  standard  for  certified  milk  is  usually  10,000 
bacteria  per  cubic  centimeter.  It  is  only  by  the  exercise  of 
the  greatest  care  at  every  point  that  the  bacterial  content 
can  be  kept  below  this  maximum. 

The  term  ''certified  milk"  has  been  registered  by  Mr. 
Francisco  of  New  Jersey,  who  was  the  first  to  engage  in 
the  production  of  such  milk  under  the  direction  of  the 
IVfedical  Milk  Commission  of  Essex  County,  New  Jersey. 
The  use  of  the  term  is  allowed  when  the  milk  is  produced 
under  the  regulation  of  any  medical  milk  commission. 

Most  certified  milk  is  now  produced  on  fancy  dairy  farms 
conducted  by  wealthy  men.  The  barns  and  other  equip- 
ment are  the  best  that  can  be  obtained,  and  the  methods 
employed,  as  far  as  cleanliness  is  concerned,  are  extreme. 
In  some  of  the  dairies  the  bacterial  content  is  reduced  to  a 
few  hundred  per  cubic  centimeter,  or  to  that  which  is  de- 
rived from  the  interior  of  the  udder.  Such  milk  will, 
when  well  refrigerated,  keep  for  long  periods  of  time.  It 
is  a  not  uncommon  thing  for  such  milk  to  keep  perfectly 
sweet  for  from  ten  to  fifteen  days. 

Pasteurization  of  market  milk. — Milk  may  become  con- 
taminated with  pathogenic  bacteria  from  a  multitude  of 
sources,  none  of  which  can  be  guarded  against  perfectly. 
It  is  estimated  that  at  least  one  person  in  each  thousand  is 
a  ''typhoid  carrier."  It  is  impossible  to  detect  which  in- 
dividuals are  a  menace  to  their  fellow  men  in  this  respect. 
Even  when  a  typhoid  carrier  is  detected,  it  is  difficult  to 
control  his  movements  so  that  he  will  not  present  a  danger 
to  those  with  whom  he  may  be,  directly  or  indirectly,  as- 
sociated. 

The  larger  cities  have  realized  the  impossibility  of  using 
the  tuberculin  test  as  a  means  of  protection  against  bovine 


CONTROL  OF  FOODS  235 

tuberculosis.  The  magnitude  of  the  task  of  testing  all  of 
the  milch-cows  each  year,  the  expense  connected  therewith, 
and  the  imperfection  of  the  protection  have  led  to  the 
abandonment  of  the  demand  for  the  tuberculin  testing  of 
all  cattle.  The  presence  of  dangerous  cases  of  udder  inflam- 
mation may  never  be  recognized  until  the  epidemic  of  septic 
sore  throat  is  well  under  way. 

Under  the  most  ideal  system  of  inspection,  the  safety  of 
large  supplies  of  milk  can  not  be  assured.  The  pasteur- 
ization of  the  milk  offers  an  effective  solution  of  this  prob- 
lem of  healthfulness  of  market  milk.  The  process  is  almost 
a  necessity  under  modern  conditions  as  a  preservative  meas- 
ure. Without  it  the  provisioning  of  our  great  cities  would 
be  most  difficult,  and  in  some  cases  impossible.  For  all  of 
these  reasons  the  introduction  of  the  pasteurization  process 
has  been  rapid,  until  more  than  90  per  cent,  of  the  milk 
sold  in  large  cities  is  now  pasteurized. 

As  previously  mentioned,  heating  causes  certain  changes 
in  milk.  In  the  treatment  of  market  milk  it  is  desirable 
to  use  as  low  temperatures  as  will  suffice  to  destroy  the 
disease-producing  bacteria.  It  is  fortunate  that  tempera- 
tures that  will  insure  this  result  have  little  effect  on  the 
milk.  The  State  of  New  York  requires  that  the  milk  shall 
be  subjected  to  a  temperature  of  from  142°  to  145°  F.  for 
not  less  than  thirty  minutes,  and  immediately  cooled.  The 
acid-forming  bacteria  are  not  completely  destroyed,  and 
the  pasteurized  milk  as  a  rule  will  undergo  the  same  type 
of  fermentation  as  raw  milk.  It  is,  however,  deemed  essen- 
tial that  all  pasteurized  milk  be  sold  as  such;  that  it  be 
delivered  to  the  consumer  within  twenty-four  hours  after 
pasteurization ;  and  that  no  milk  be  pasteurized  a  second 
time. 

The  continuous  pasteurizing  machines  have  the  disadvan- 
tage that  a  small  portion  of  the  milk  passes  through  so 


236  AGRICULTURAL  BACTERIOLOGY 

quickly  that  all  pathogenic  bacteria  therein  might  not  be 
destroyed  (p.  181).  This  has  led  to  the  use  of  the  "hold- 
ing" process,  in  which  the  milk  is  heated  to  the  desired 
temperature  and  then  placed  in  tanks,  where  it  remains  at 
this  temperature  for  any  desired  time.  Every  portion  is 
thus  treated  in  a  uniform  manner. 

If  the  milk  is  bottled  after  pasteurization,  there  remains 
opportunity  for  reinfection,  possibly  with  typhoid  bacilli. 
Pasteurization  in  the  final  container,  the  bottle,  is  being 
recommended.  This  is  possible  only  when  a  special  bottle 
is  used,  having  a  metal  cap  lined  with  paper,  or  some  other 
special  appliance. 


PART  IV 
TRANSMISSIBLE  DISEASES 


CHAPTER  XIX 

THE  RELATION  OF  MICROORGANISMS  TO 
DISEASES  OF  ANIMALS 

Communicable  diseases. — The  diseases  of  animals  may  be 
divided  into  two  classes:  the  organic  or  constitutional, 
which  are  due  to  the  faulty  operation  of  some  organ;  and 
the  communicable,  which  are  caused  by  the  invasion  of  the 
body  by  some  organism  and  the  growth  thereof  with  the 
formation  of  substances  that  have  a  harmful  action  on  the 
body.  The  latter  are  termed  communicable  diseases,  be- 
cause the  passage  of  the  causal  organism  from  the  diseased 
to  the  healthy  animal  is  sufficient  to  spread  the  trouble. 
The  organic  diseases  can  not  be  thus  transmitted,  for  they 
are  not  due  to  the  presence  of  a  living  organism  in  the 
body.  The  communicable  diseases  are  also  termed  infec- 
tious, contagious,  and  preventable,  since  the  prevention  of 
their  spread  can  be  accomplished  by  stopping  the  trans- 
mission of  the  organism.  In  some  instances  the  knowledge 
of  the  manner  of  transmission  is  so  complete  that  if  stock- 
men could  be  induced  to  put  that  knowledge  into  practice 
the  diseases  would  soon  disappear,  while  in  other  cases  the 
information  is  not  yet  sufficiently  complete  to  enable  their 
spread  to  be  prevented. 

Such  transmissible  diseases  as  tuberculosis,  contagious 
abortion,  hog  cholera,  Texas  fever,  and  glanders  entail 
an  enormous  tax  on  the  livestock  industry  of  the  world,  as 
will  appear  in  the  discussion  of  the  specific  diseases.  Since 
the  prevention  of  disease  is  a  problem  that  must  always 
rest  in  the  hands  of  the  farmer  himself,  rather  than  in  any 

239 


240  AGRICULTURAL  BACTERIOLOGY 

professional  aid  he  may  employ,  it  is  desirable  that  every 
stockman  be  acquainted  with  the  salient  facts  concerning 
the  more  important  of  the  transmissible  diseases  of  domestic 
animals,  just  as  everyone  should  know  something  of  the  im- 
portant transmissible  diseases  of  man,  so  that  he  may  intel- 
lig-ently  protect  himself  from  them. 

Infection. — In  order  to  produce  disease  the  organism 
must  invade  the  body,  must  grow  therein,  and  its  by-pro- 
ducts must  exert  an  injurious  effect  on  the  body  tissues. 
This  sequence  of  events  is  known  as  infection.  The  severity 
of  the  attack  of  any  communicable  disease  may  vary  from 
one  animal  to  another,  owing  to  the  difference  in  resistance 
of  the  host  and  to  a  difference  in  the  virulence  of  the  or- 
ganism, which  may  be  defined  as  the  power  of  the  organism 
to  multiply  within  the  body  and  produce  disease.  Little 
is  known  of  the  conditions  that  increase  or  diminish  the 
virulence  of  organisms  in  nature.  The  resistance  of  the 
host  may  be  impaired  by  any  condition  that  tends  to  weaken 
the  bod}^,  such  as  fatigue,  exposure  to  cold,  heat,  or  damp- 
ness, improper  diet,  thirst,  age,  wounds,  and  other  dis- 
eases. Neither  the  invading  organism  nor  the  host  are 
to  be  considered  as  passive  agents.  The  relation  between 
them  is  a  true  struggle,  a  fight  to  the  finish.  In  the  strug- 
gle the  host  seeks  to  overcome  the  parasite  by  means  that 
will  be  discussed  later,  and  the  organism  protects  itself  in 
the  progress  of  its  growth  and  development.  In  so  doing 
the  perpetuation  of  the  species  is  accomplished. 

The  portals  of  entry  into  the  body  are  the  broken  skin, 
or  an  injured  mucoias  membrane,  the  alimentary  tract,  the 
respiratory  tract,  the  genital  tract,  and  the  conjunctiva, 
or  the  mucous  membrane  of  the  eye.  Many  organisms  have 
specific,  definite  methods  by  which  they  enter  the  body  of 
the  host;  for  example,  the  hog  cholera  organism  enters  by 
way  of  the  alimentary  tract,   while  the  tubercle  bacillus 


INFECTION  241 

enters  in  a  variety  of  ways,  as  through  wounds,  by  inhala- 
tion, or  by  ingestion.  The  tetanus  or  lockjaw  bacillus  is 
always  introduced  through  wounds  of  the  skin  or  of  the 
mucous  membrane. 

The  original  or  initial  infection  is  called  the  primary  in- 
fection, and  may  be  followed  by  a  second  invasion  with 
another  kind  of  organism  which  may  have  been  present  in 
the  body,  but  which  was  unable  to  multiply  until  the  re- 
sistance was  first  lowered  by  the  primary  infection.  Infec- 
tion is  usually  due  to  a  single  specific  organism,  but  some 
troubles  are  due  to  a  mixed  infection  with  two  or  more  or- 
ganisms. When  the  body  has  been  weakened  by  organic 
diseases,  it  is  sometimes  more  susceptible  to  invasion  by 
certain  disease-producing  organisms,  or  the  results  of  such 
invasion  are  more  likely  to  be  serious.  The  original  trouble 
might  have  resulted  in  death,  but  the  end  is  hastened  by 
the  terminal  infection,  as  it  is  called. 

The  invading  organisms  injure  the  tissues  by  the  pro- 
duction of  poisonous  substances  known  as  toxins.  In  some 
cases  the  organisms  grow  in  a  limited  area,  and  do  not  cause 
any  great  destruction  of  the  tissue  at  the  point  of  growth ; 
but  the  toxin  is  so  active  that  a  minute  quantity  is  suffi- 
cient to  cause  death.  Such  a  disease  is  known  as  toxemia, 
in  contradistinction  to  the  hacteremia  or  septic(Bmia,  in 
which  the  entire  bod}^  is  invaded  by  the  organism,  as  in  the 
ease  of  anthrax.  Examples  of  toxemias  are  lockjaw  and 
diphtheria.  In  still  other  instances  the  invasive  powers  of 
the  organisms  are  not  great,  but  the  tissue  is  destroyed  at 
the  point  of  growth,  as  in  the  case  of  the  pus-producing 
organisms. 

It  is  evident  that  the  symptoms  of  any  disease  can  not 
appear  until  the  organism  has  had  time  to  multiply  and  to 
form  sufficient  toxin  to  have  a  visible  effect  on  the  body 
of  the  animal.     This  period  which  may  vary  from  a  few 


242  AGRICULTURAL  BACTERIOLOGY 

days  to  several  months  is  called  the  period  of  incubation 
of  the  disease.  The  changes  in  the  various  tissues  due  to 
the  action  of  the  organism  are  called  the  lesions  of  the  dis- 
ease. With  some  diseases  they  are  very  characteristic,  in 
others  not. 

The  external  defenses  of  the  body. — There  are  many 
means  by  which  nature  has  sought  to  protect  the  body 
against  the  invasion  of  microorganisms.  The  surface  of  the 
body  is  covered  by  the  skin,  and  all  of  the  cavities  of  the 
body  that  are  in  contact  with  the  exterior  are  provided  with 
a  mucous  membrane.  The  bacteria  normally  gain  entrance 
with  but  few  exceptions  through  these  protective  mem- 
branes, only  as  they  are  injured.  The  mucous  membranes 
are  always  bathed  with  the  products  of  glandular  activity, 
which  possess  a  more  or  less  marked  germicidal  or  antiseptic 
action.  By  reason  of  this  many  of  the  organisms  that  come 
in  contact  with  these  fluids  are  thus  destroyed.  Wounds  in 
the  mouth  and  in  the  intestine  must  of  necessity  frequently 
occur,  especially  with  animals  that  feed  on  coarse,  dry 
fodder.  Yet  a  harmful  effect  from  such  a  source  is  rarely 
noted.  The  lungs  and  air  passages  are  constantly  exposed 
to  dust  laden  with  adherent  bacteria.  These  foreign  bodies 
are  removed  by  the  action  of  the  cilia  of  the  cells  lining  the 
air-passages.  The  hairlike  appendages  are  constantly  in 
motion  and  tend  to  move  any  foreign  particle  outward. 

The  internal  defenses. — After  the  microorganisms  have 
invaded  the  tissues,  their  development  can  not  go  on  un- 
hampered, for  the  body  has  a  number  of  internal  defenses 
that  must  be  overcome  before  growth  and  disease  produc- 
tion can  occur.  An  animal  is  said  to  be  immune  to  a  dis- 
ease when  it  resists  the  development  of  the  organism,  or  is 
not  injured  by  the  poison  that  the  organism  produces. 
Various  explanations  have  been  offered  to  explain  the  im- 
munity of  animals.     The  white   blood   corpuscles  possess 


IMMUNITY  243 

amoeboid  properties,  and  are  able  to  ingest  solid  bodies 
like  the  bacteria  and  digrest  them.  This  process  is  known 
as  phagoc3'tosis,  and  such  devouring  cells  are  called  phag- 
ocytes. Whenever  any  portion  of  the  body  is  invaded  by 
a  foreign  agent,  or  when  any  abnormal  condition  arises,  the 
phagocytes  are  attracted  to  this  point  as  a  result  of  a  chem- 
ical stimulus.  This  causes  them  to  accumulate  at  or  near 
the  point  of  invasion,  where  they  soon  engulf  and  destroy 
many  of  the  invading  organisms.  If  these  white  blood  cor- 
puscles are  able  to  overcome  the  harmful  bacteria,  the  ini- 
tial infection  may  .be  rendered  of  no  importance.  Again, 
the  organism  may  multiply  and  form  poisonous  products 
which  may  injure  the  body  to  the  extent  that  death  is 
caused,  or,  under  the  stimulus  of  these  harmful  products, 
the  body  cells  may  react  and  form  substances  that  neutralize 
or  nullify  in  some  way  the  poisonous  effects  of  the  pt*oducts 
of  the  organism.  These  antagonistic  and  protective  pro- 
ducts are  diffused  through  the  liquids  of  the  body,  especially 
in  the  blood  serum  and  form  the.  basis  of  the  anti-serums 
that  are  used  for  protective  purposes. 

Immunity. — A  specific  disease  may  occur  only  in  a  single 
host  species,  as  in  hog  cholera,  or  it  may  be  capable  of 
spreading  throughout  a  variety  of  different  animals.  Black- 
leg affects  only  cattle  and  sheep,  while  the  anthrax  bacil- 
lus produces  a  characteristic  disease  in  man  as  well  as  in 
many  of  the  lower  animals.  Numerous  diseases  affecting 
man,  such  as  typhoid  fever,  diphtheria,  yellow  fever,  and 
cholera,  are  limited  to  this  host  alone.  Other  warm-blooded 
animals  are  naturally  insusceptible  to  these  maladies;  they 
possess  a  natural  immunity. 

The  term  natural  immunity  is  applied  to  that  condition 
which  enables  an  animal  to  resist  the  natural  invasion  by 
organisms  that  attack  other  varieties  or  species  of  animals. 
It  is  a  condition  that  is  present  at  birth,  continues  through- 


244  AGRICULTURAL  BACTERIOLOGY 

out  life,  and  is  transmitted  to  the  offspring.  A  striking 
example  of  natural  immunity  is  that  of  Algerian  sheep  to 
anthrax,  while  other  varieties  are  very  susceptible  to  this 
disease. 

Immunity  to  a  disease  may  be  established  in  the  indi- 
vidual after  birth.  It  is  then  called  acquired  immunity. 
The  lessened  susceptibility  to  certain  diseases  with  increas- 
ing age  is  an  example,  as  is  noted  in  measles,  chickenpox, 
and  whooping-cough  in  human  beings,  and  with  blackleg 
in  cattle. 

The  immunity  that  is  conferred  by  resisting  successfully 
an  attack  of  infectious  disease  is  another  example.  In- 
stances of  this  type  of  acquired  immunity  are  noted  in 
smallpox  and  yellow  fever  in  man,  in  Texas  fever  in  cattle, 
and  in  cholera  in  hogs.  The  period  of  persistence  of  the 
acquired  immunity  is  variable,  sometimes  extending  through 
the  remainder  of  the  life  of  the  individual,  or  again  persist- 
ing but  a  short  time.  A  successful  recovery  from  some 
diseases  does  not  seem  to  convey  any  immunity  against 
second  attack.  Acquired  immunity  may  also  be  produced 
artificially  in  a  number  of  wa^^s  which  may  be  summarized 
as  follows : 

By  inoculating  the  individual  with  such  a  small  number 
of  organisms  that  a  fatal  attack  of  the  disease  will  not 
result.     This  method  is  used  in  the  case  of  Texas  fever. 

By  inoculating  with  an  attenuated  or  weakened  organism. 
This  is  practiced  in  anthrax,  blackleg,  rabies,  and  bubonic 
plague  in  man. 

By  inoculating  with  an  organism  that  has  been  modified 
by  passage  through  another  species  of  animal.  This  method 
is  illustrated  by  vaccine  for  smallpox. 

By  the  injection  of  toxins.  This  is  used  in  the  immuni- 
zation of  animals  against  the  virus  of  a  disease  for  the  pur- 


IMMUNITY  245 

pose  of  securing  antitoxins  from  their  blood,  as  in  the  prep- 
aration of  diphtlieria  antitoxin. 

By  the  injection  of  antitoxins.  These  are  used  to  pro- 
tect against  toxins  and  natural  infection,  as  in  the  case  of 
diphtheria. 

By  the  injection  of  blood  serum  from  immune  or  hyper- 
immune animals  for  preventive  purposes.  The  serum  used 
in  the  case  of  hr>i:  cholfTci  is  an  example. 

Active  and  Passive  Immunity. — If  the  organism  of  the 
disease  is  concerned  directly  in  the  process  of  bringing 
about  the  production  of  the  anti-bodies,  the  immunity  is 
termed  active.  An  immunity  that  is  due  to  recovery  from 
a  natural  attack  is  active,  as  is  that  produced  by  injecting 
the  organism  or  its  toxins  into  the  body.  Active  immunity 
is  slow  in  its  development,  is  somewhat  dangerous,  and  is 
always  attended  with  some  discomfort  to  the  person  or  ani- 
mal in  which  it  is  produced.  It  persists,  as  a  rule,  for  a 
considerable  period,  varying  from  a  few  weeks  to  several 
years. 

If  the  blood  serum  of  an  animal  that  has  an  active  im- 
munity to  a  disease  is  injected  into  an  animal  that  is  sus- 
ceptible to  the  disease,  an  immunity  is  produced  which  is 
called  passive  immunity.  It  involves  no  activity  of  the 
tissues  of  the  immunized  animal.  The  passively  immunized 
animal  is  simply  the  recipient  of  substances  formed  in  the 
bodies  of  other  animals  and  transferred  to  it.  Passive  im- 
munity is  rapidly  produced,  and  is  attended  with  little 
danger  and  discomfort.  The  period  of  protection  is  meas- 
ured by  a  few  days  or  weeks.  The  most  extensive  use  of 
passive  immunity  is  in  hog  cholera,  tetanus,  and  diphtheria. 

It  is  a  well  known  fact  that  some  outbreaks  of  a  disease 
are  very  severe  in  that  many  of  the  infected  die,  while  in 
another  outbreak  of  the  same  disease  practically  all  of  the 


246  AGRICULTURAL  BACTERIOLOGY 

infected  individuals  recover.  This  can  not  be  explained  by 
the  greater  resistance  of  the  second  group  over  the  first,  but 
rather  the  explanation  is  to  be  sought  in  the  diminished 
virulence  of  the  organism.  As  has  been  stated,  the  causes 
that  induce  such  changes  in  nature  are  not  known. 

The  first  effort  to  impart  immunity  by  artificial  means 
was  by  the  intentional  inoculation  of  individuals  with  ma- 
terial taken  from  mild  cases  of  smallpox.  The  mild  attack 
thus  induced  afforded  protection  to  the  individual  against 
the  more  severe  form  of  the  disease.  Later  it  was  noted  by 
Jenner,  an  English  surgeon,  that  those  individuals  that 
had  acquired  cowpox  by  milking  a  cow  suffering  from  this 
trouble  were  thereby  protected  against  smallpox.  Follow- 
ing this  observation,  the  inoculation  of  human  virus  against 
smallpox  was  superseded  by  vaccination  with  material  taken 
from  the  pustules  of  the  animal  disease,  cowpox,  or  vaccinia, 
as  it  is  called. 

It  is  now  known  that  the  organism  causing  cowpox  is  a 
modified  form  of  the  smallpox  virus.  In  some  manner  its 
residence  in  the  body  of  cattle  has  so  changed  its  properties 
that  it  is  no  longer  able  to  produce  a  dangerous  form  of  the 
disease  in  man,  but  it  is  able  to  stimulate  the  tissues  to 
manufacture  sufficient  anti-bodies  to  protect  the  body  for 
a  number  of  years  against  a  natural  attack.  The  vaccine 
used  for  inoculation  contains  the  virus  of  smallpox,  the  na- 
ture of  which  is  unknown. 

All  vaccines  that  are  used  as  a  protective  measure  against 
any  contagious  disease  contain  the  virus  of  the  disease 
against  which  protection  is  sought.  The  virus  may  be  viru- 
lent ;  it  may  be  attenuated  or  weakened ;  or  it  may  be  dead. 
The  degree  of  protection  afforded  by  the  vaccination  pro- 
cess will  depend  on  the  extent  to  which  the  organism  has 
been  attenuated.  Thus  the  protection  afforded  by  ''killed" 
organisms  is  not  so  great  as  when  the  weakened  organisms 


IMMUNITY  247 

are  used.  In  the  case  of  human  vaccination,  "killed"  cul- 
tures are  usually  employed,  because  of  the  possibility  that 
the  virulence  of  the  weakened  org:anism  may  accidentally  be 
regained.  The  organisms  are  killed  in  such  a  way  as  to  de- 
stroy their  reproductive  power,  but  not  to  change  them 
chemically  to  such  an  extent  that  when  introduced  into  the 
body  they  will  not  stimulate  the  cells  to  the  production  of 
the  anti-bodies.  The  manner  in  which  the  different  vac- 
cines are  made  will  be  discussed  in  the  treatment  of  the 
specific  diseases.  Vaccines  are  used  not  only  to  prevent  but 
also  to  cure  disease. 

In  the  production  of  passive  immunity  the  anti-bodies 
are  transferred  from  the  body  of  the  animal  in  which  they 
have  been  actively  formed  to  the  animal  to  be  protected. 
This  transfer  is  accomplished  by  withdrawing  a  portion 
of  the  blood  from  the  immune  animal  and  injecting  it  into 
the  animal  that  it  is  sought  to  protect.  Since  the  blood 
serum  is  used,  the  term  protective  serum  or  anti-serum  is 
often  used.  In  many  instances  the  anti-serum  contains 
I)rimarily  a  substance  that  neutralizes  the  toxin.  The  term 
antitoxin  is  therefore  often  used. 

The  blood  of  a  hog  that  has  recovered  from  hog  cholera 
will  contain  sufficient  anti-bodies  to  protect  the  individual 
against  a  subsefjuent  attack,  but  not  a  sufficient  amount 
so  that  the  ])lood  would  bestow  any  marked  degree  of  protec- 
tion on  another  animal  when  inoculated  with  an  amount 
that  would  be  practicable  to  use.  In  order  to  make  the 
method  of  practical  value,  the  immune  animal  is  forced  to 
manufacture  a  larger  amount  of  the  anti-bodies  than  would 
normally  be  produced.  An  animal  so  treated  is  said  to  be 
hyper-immiinized.  In  preparing  hog-cholera  serum,  this 
is  accomplished  by  injecting  into  the  body  of  the  immune 
hog  a  large  quantity  of  blood  from  a  hog  that  is  already 
sick  with  hog  cholera.     The  specific  organism  causing  hog 


248  AGRICULTURAL  BACTERIOLOGY 

cholera  is  yet  unknown,  although  it  can  be  transferred 
by  the  use  of  blood  from  a  sick  hog.  The  introduction  of 
a  large  quantity  of  the  virus  into  the  body  of  the  immune 
hog  causes  the  formation  of  an  increased  amount  of  the 
protective  bodies.  The  immunizing  process  is  thus  repeated 
until  the  blood  contains  such  a  quantity  of  protective  sub- 
stances that,  when  transferred  in  practicable  amounts,  it 
imparts  a  considerable  degree  of  immunity. 

The  disease  virus  is  obtained  from  a  sick  hog  by  bleeding 
from  the  throat.  This  virulent  blood  is  usually  introduced 
into  the  blood  vessels  of  the  animal  to  be  hyper-immunized, 
which,  when  its  blood  is  sufficiently  high  in  the  protective 
bodies,  is  bled  for  the  anti-serum  by  cutting  off  a  piece  of 
the  tail.  The  animal  can  be  bled  several  times  in  this  way, 
a  fresh  cut  being  made  each  time  until  this  appendage  is  too 
short  for  further  use.  The  final  bleeding  is  then  made 
from  the  throat. 

In  the  preparation  of  diphtheria  antitoxin  the  horse  is 
used  to  produce  the  anti-bodies.  The  animal  is  not  suscep- 
tible to  diphtheria;  hence,  the  organisms  themselves  can 
not  be  employed  to  stimulate  the  production  of  anti-bodies. 
The  horse  is,  however,  susceptible  to  the  toxin  of  the  diph- 
theria organism.  The  organism  is  grown  in  the  laboratory 
in  beef  broth,  which  is  tittered  through  porcelain  to  remove 
all  the  bacteria,  and  gradually  increasing  doses  of  this  fil- 
trate are  then  injected  into  the  body  of  the  horse.  At 
first  only  very  small  doses  can  be  administered  without 
killing  the  animal;  but  after  recovery  from  the  first  injec- 
tion, repeated  doses  of  increasing  amounts  are  applied, 
the  effect  of  which  is  to  produce  the  protective  anti-bodies 
in  the  blood  of  the  animal.  The  blood  is  then  drawn 
from  the  jugular  vein ;  it  is  allowed  to  coagulate  in  order 
to  remove  the  clot,  and  the  blood  serum  is  used.  Not  only 
does  this  serum  protect  an  individual  from  acquiring  diph- 


IMMUNITY  249 

theria  by  rendering  him  artificially  immune,  but  it  acts 
as  a  curative  agent  in  neutralizing  the  poison  of  the  disease 
if  applied  in  the  earlier  stages  of  the  disease. 

The  blood  serum  of  animals  hyper-immunized  against  hog 
cholera  or  diphtheria  varies  greatly  in  the  amount  of  anti- 
bodies formed.  Before  it  is  used  it  is  necessary  to  know 
something  of  the  strength  or  potency  of  the  serum,  so  that 
the  proper  quantity  to  be  used  in  the  animal  to  be  pro- 
tected may  be  determined.  This  is  accomplished,  in  the 
case  of  hog  cholera,  by  inoculating  a  number  of  young  pigs 
with  a  definite  (piantity  of  the  disease  virus  and  a  varying 
amount  of  the  protective  serum,  noting  the  amount  which 
is  required  to  protect  the  animal  against  the  artificial  in- 
oculation. 

In  the  case  of  diphtheria  and  tetanus  antitoxin  a  num- 
ber of  guinea-pigs  are  inoculated  with  a  definite  amount 
of  toxin  and  with  varying  amounts  of  antitoxin.  If  the 
antitoxin  administered  to  a  particular  individual  is  suffi- 
cient to  neutralize  the  toxin,  the  animal  remains  alive.  If 
the  toxin  is  in  excess,  the  animal  dies. 

Persistence  of  immunity. — Passive  immunity,  produced 
by  the  transfer  of  the  anti-bodies,  is  always  of  short  dura- 
tion as  compared  with  the  active  immunity  produced  by  ar- 
tificial means,  while  the  active  immunity  produced  as  a  re- 
sult of  the  natural  cause  of  the  disease  persists  for  a  still 
longer  period.  The  variation  in  time  during  which  pro- 
tection persists  must  be  taken  into  account  in  the  practical 
employment  of  serums  and  vaccines  in  the  prevention  of  an- 
imal diseases. 

Exit  of  organisms  from  body. — Almost  without  excep- 
tion, the  pathogenic  organisms  grow  only  in  the  bodies  of 
susceptible  animals.  Their  continued  existence  in  nature 
is  therefore  dependent  upon  their  expulsion  from  the  dis- 
eased body,  and  the  opportunity  for  introduction  into  a 


250  AGRICULTURAL  BACTERIOLOGY 

new  susceptible  host.  The  exits  from  the  host  by  which  or- 
g-anisms  find  their  way  to  new  hosts  vary  in  the  different 
diseases.  In  intestinal  diseases,  as  hog  cholera,  the  excreta 
serve  as  a  mode  of  exit.  In  tuberculosis  the  secretions, 
as  milk  and  saliva,  function  as  carriers  of  contagion.  In 
some  diseases  the  blood  from  wounds  caused  by  biting  in- 
sects or  the  discharges  from  abscesses  on  the  surface  of  the 
body  serve  as  channels  of  transmission. 

The  transfer  of  the  causal  organisms  from  one  animal  to 
another  may  take  place  in  a  multitude  of  ways.  In  the 
same  herd  a  healthy  animal  easily  comes  in  direct  contact 
with  the  infectious  material  from  a  diseased  animal.  The 
spread  of  the  disease  to  other  herds  may  take  place  through 
the  transfer  of  an  infected  animal  or  of  infectious  material, 
such  as  milk  or  contaminated  objects.  The  direct  methods 
of  transfer  can  be  readily  guarded  against,  but  the  more 
indirect  modes  of  transmission  are  much  more  difficult  to 
detect.  Thus  hog-cholera  virus  can  be  readily  transferred 
by  dogs,  crows,  or  persons  carrying  the  virus  on  their  feet. 

The  opportunity  for  the  transfer  of  organisms  for  any 
considerable  distance  is  dependent  on  the  resistance  of  the 
organism,  w^hich  is  largely  determined  by  the  fact  as  to 
whether  it  produces  spores  or  not.  Most  of  the  non-spore- 
forming  organisms  can  not  persist  for  any  long  period  out- 
side the  animal,  since  they  succumb  quite  readily  to  such 
unfavorable  environmental  influences  as  drying,  sunlight, 
and  the  action  of  saprophytic  bacteria.  The  spore-forming 
organisms,  on  the  other  hand,  can  persist  for  long  periods, 
owing  to  the  resistance  of  the  spores  to  all  ordinary  environ- 
mental conditions. 

The  prevention  of  the  transmissible  diseases  involves  the 
keeping  of  the  causal  organisms  from  coming  in  contact 
with  healthy  animals.  This  can  be  accomplished  by  isola- 
tion of  diseased  animals,  by  the  disinfection  of  their  secre- 


IMMUNITY  251 

tions  and  the  objects  with  which  they  have  been  in  contact, 
and  by  the  proper  disposal  of  tlieir  bodies.  A  personal 
knowledge  of  the  nature  of  the  organism  and  of  its  method 
of  distribution  is  the  only  thing  that  enables  one  to  protect 
himself  or  his  herds  and  flocks. 

Necessity  for  correct  diagnosis. — It  is  very  essential  that 
a  correct  diagnosis  of  any  of  the  transmissible  diseases  be 
made,  for  the  methods  that  will  prove  effective  against  one 
may  have  no  effect  against  another.  Especially  is  this  true 
when  serums  or  vaccines  are  to  be  used  in  preventing  fur- 
ther spread,  for  these  substances  are  specific  in  their  action. 
The  farmer  must  usually  rely  on  the  experienced  veterin- 
arian for  a  proper  diagnosis  of  any  transmissible  disease, 
and  the  veterinarian  is  fre(iuently  forced  to  call  to  his  aid 
the  facilities  of  a  bacteriological  laboratory. 

The  use  of  drugs  in  the  treatment  of  the  transmissible 
diseases  is  usually  without  any  curative  effect.  The  farmer 
must  exert  himself  to  prevent  the  disease,  and  especially  to 
prevent  their  introduction  on  his  farm. 


CHAPTER  XX 

ANTHRAX,  BLACKLEG,  HEMORRHAGIC 
SEPTICEMIA,  AND  CORN-STALK  DISEASE 

Anthrax. — The  disease  commonly  known  as  anthrax  is 
one  of  th*e  most  interesting  of  the  transmissible  diseases  of 
man  and  the  lower  animals.  The  causal  organism  is  large, 
and  is  found  in  great  numbers  in  the  tissues  of  the  dead 
animal.  It  grows  profusely  on  many  kinds  of  culture 
media  of  both  animal  and  vegetable  origin.  These  facts 
led  to  its  discovery  and  cultivation  early  in  the  develop- 
ment of  bacteriology.  The  information  gained  from  a 
study  of  this  organism  was  of  the  greatest  importance  in 
the  study  of  other  and  more  obscure  diseases. 

In  1849  Pollender  noted  the  organism  in  the  blood  of 
animals  that  had  died  from  the  disease.  This  observation 
was  confirmed  by  others.  Robert  Koch,  in  1876,  cultivated 
the  organism  on  artificial  media.  He  proved  that  its  arti- 
ficial cultivation  could  be  continued  for  long  periods  of 
time,  and  that  on  reintroduction  into  the  body  of  a  suscep- 
tible animal,  a  disease  identical  in  symptoms  and  lesions 
with  the  naturally  occurring  cases  would  be  produced.  The 
causal  relation  of  bacteria  to  the  production  of  disease  was 
thus  proved  where  previously  it  had  been  suspected,  but 
not  established  with  certainty.  In  1881  Pasteur  published 
the  results  of  his  researches  on  a  method  of  protecting  ani- 
mals against  anthrax  by  vaccinating  them  with  weakened 
cultures  of  the  organism.  This  work  was  the  starting-point 
for  the  development  of  vaccines  and  other  biological  pro- 

252 


ANTHRAX  253 

ducts  that  have  been  of  inestimable  value  in  the  prevention 
and  euro  of  many  transmissible  diseases. 

The  organism. — The  anthrax  bacillus  is  one  of  the  largest 
of  the  disease-producing  bacteria.  The  rodlike  cells  have 
square-cut  ends.  In  liquid  media  the  cells  appear  in 
chains  of  great  length,  giving  to  the  growth  the  appearance 
of  a  tangled  mass  of  cotton  fibers.  The  growth  is  rapid  on 
all  of  the  ordinary  types  of  culture  media.  It  grows  under 
both  aerobic  and  anaerobic  conditions.  In  the  presence  of 
air,  spores  are  formed  quickly  and  in  great  abundance. 
The  spores  are  not  especially  resistant  to  heat,  being  killed 
in  a  few  moments  at  100°  C.  They  are,  however,  extremely 
resistant  to  desiccation,  and  also  live  for  years  in  water. 
In  the  author's  laboratory  some  spores  were  still  alive  after 
eighteen  years'  residence  in  a  sample  of  water  collected  from 
a  pond  in  a  pasture  in  which  a  number  of  animals  had  died 
of  anthrax.  The  rapidity  and  profuseness  with  which 
spores  are  produced  when  the  vegetative  cells  are  exposed 
to  air  is  of  thp  greatest  importance  in  the  distribution  and 
persistence  of  the  disease. 

The  disease  is  said  to  be  the  most  widespread,  geograph- 
ically and  zoologically,  of  all  the  transmissible  diseases.  It 
has  been  present  in  Europe  for  hundreds  of  years.  In 
1613  it  is  asserted  to  have  caused  the  death  of  fifty  thousand 
people  in  southern  Europe.  In  still  earlier  times  the  Arab 
physicians  called  it  "Persian  fire."  As  the  civilization  of 
Europe  has  spread  to  other  lands,  anthrax  has  been  one  of 
its  gifts,  until  to-day  no  part  of  the  world  in  which  stock- 
raising  is  important  is  free  from  it.  In  this  country  it  has 
been  reported  in  many  of  the  States. 

The  organism  is  one  that  is  easily  transported  over  long 
distances  in  time  and  space,  due  to  its  resistant  spores, 
which  are  likely  to  be  present  on  many  articles  of  commerce, 
such  as  hair,  wool,  bristles,  and  hides.     Many  of  the  out- 


254  AGRICULTURAL  BACTERIOLOGY 

breaks  in  both  animals  and  man  in  this  country  have  been 
caused  by  animal  products  from  the  Orient  and  South 
America. 

The  disease  is  primarily  one  of  cattle,  sheep,  goats,  horses, 
and  less  frequently  hogs.  The  other  common  domestic  an- 
imals of  our  country,  cats,  dogs,  and  fowls,  are  relatively 
immune,  acquiring  the  disease  only  when  exposed  to  large 
doses  of  the  organism,  as  is  the  case  when  meat  from  an 
anthrax  carcass  is  eaten.  Man  is  also  susceptible  to  the 
disease.  He  is,  however,  more  resistant  to  it  than  are  the 
ruminants,  both  domestic  and  wild. 

The  disease  is  variously  known  in  its  several  forms.  The 
old  English  term  for  it  was  murrain.  Splenic  fever  refers 
to  the  enlarged  condition  of  the  spleen,  while  malignant 
carbuncle  refers  to  the  appearance  of  large  swellings  on 
the  surface  of  the  body,  a  common  manifestation  of  the 
disease  in  man  when  the  organism  has  been  introduced 
into  wounds. 

Infection. — In  the  case  of  cattle,  sheep,  and  horses,  the 
portal  of  entry  is  most  frequently  the  alimentary  tract.  It 
is  supposed  that  the  compound  stomach  of  the  ruminating 
animal  gives  opportunity  for  the  growth  of  the  organism 
and  for  the  more  frequent  infection  of  this  type  of  animal. 
It  seems  probable  that  the  organism  can,  in  many  cas' c 
pass  through  the  uninjured  wall  of  the  intestine.  It  is  cer- 
tain that  its  entrance  is  made  more  easy  and  certain  by 
the  presence  of  woui.ds  in  any  part  of  the  alimentary  tract. 
It  is  probable  that  abrasion  of  the  mucous  surfaces  in  the 
mouths  of  grazing  animals  or  those  fed  on  dry  fodder  read- 
ily permits  of  the  entrance  of  the  organism.  The  transfer- 
ence of  the  organism  from  infectious  material  and  its  intro- 
duction into  the  body  may  be  accomplished  by  b'ting  flies. 

It  is  believed  that  this  is  the  chief  way  in  which  the  horses 
and  mules  of  the  plantations  in  the  Mississippi  delta  region 


ANTHRAX  255 

become  infected.  The  infection  may  occur  by  grazing  on 
infected  pastures  and  by  the  use  of  contaminated  dry  fod- 
der, the  spore  enabling  the  organism  to  persist  on  the  dry 
material. 

Before  the  development  of  the  procedure  for  protective 
vaccination,  the  disease  occurred  yearly  on  many  farms  in 
France.  These  were  known  as  "anthrax  farms."  The 
continued  persistence  of  the  organism  in  the  soil  of  a  con- 
taminated field  is  usually  ascribed  to  the  resistant  powers 
of  the  spores.  It  may  be  that  growth  may  occur  each  sum- 
mer in  the  soil,  a  new  crop  of  spores  being  thus  produced 
to  favor  the  continued  existence  of  the  organisms.  Its 
more  frequent  and  constant  appearance  in  stock  pastured 
on  low,  moist  land  is  evidence  of  the  growth  of  the  organ- 
ism under  these  conditions.  The  contamination  of  stables, 
yards,  or  fields  with  anthrax  bacilli  is  certain  to  make  them 
unsafe  for  a  number  of  years. 

Symptoms. — The  rapidity  of  progress  of  the  disease  in 
the  individual  has  led  to  the  division  of  the  various  cases 
into  three  types:  the  peracute,  the  acute,  and  the  subacute. 
In  the  first  the  animal  may  show  no  visible  symptoms  until 
a  few  hours  before  death.  Indeed,  so  rapid  is  the  progress 
of  the  disease  that  the  usual  yield  of  milk  may  be  obtained 
at  one  milking  and  death  occur  before  the  next  milking- 
time.  An  artificially  infected  guinea-pig  may  show  no  vis- 
ible symptoms  two  hours  before  death.  The  temperature 
may  reach  106°  F.  in  the  absence  of  all  other  symptoms. 
With  such  a  temperature  the  respiration  will  be  increased 
and  the  heart-beats  so  pronounced  that  they  may  be  heard. 
Later  the  animal  becomes  weak  and  stupid,  and  the  temper- 
ature falls  to  subnormal. 

In  the  acute  type  sj'mptoms  of  nervousness  are  present, 
manifested  by  kicking  and  convulsions.  The  visible  mucous 
membranes  become  bluish  and  the  urine  is  often  bloody.     In 


256  AGRICULTURAL  BACTERIOLOGY 

the  subacute  type  the  duration  of  the  disease  is  from  one 
to  seven  days.  Tumors  or  carbuncles  are  quite  common. 
They  usually  appear  on  the  shoulders  and  neck,  and  are 
due  to  the  bruising  of  the  parts,  which  injury  gives  rise  to 
a  collection  of  the  bacilli  within  the  blood-vessels  of  the 
parts,  inducing  inflammation,  followed  by  the  development 
of  the  tumor.  Carbuncles  may  also  be  occasioned  by  in- 
fection through  a  wound. 

The  subacute  type  is  the  most  common,  and  is  the  only 
form  that  can  be  treated.  It  is  also  the  type  noted  in  most 
isolated  cases  of  anthrax.  At  the  beginning  of  an  outbreak 
the  first  animals  lost  usually  show  few  or  no  symptoms. 
This  rapid  progress  of  the  disease  may  be  due  to  the  lack 
of  resistance  of  the  animal.  Such  rapid  progress  of  the 
disease  often  leads  to  suspicion  of  poisoning,  or  to  death  by 
lightning.  Such  conclusions  as  to  the  cause  of  death  may 
lead  to  the  careless  disposal  of  the  carcass,  thus  endangering 
human  life  as  well  as  causing  a  widespread  outbreak,  not 
only  on  the  farm  but  in  the  neighborhood.  It  is  well  to 
consider  all  cases  of  sudden  death  in  an  animal,  especially 
when  no  definite  cause  can  be  given,  as  due  to  dangerous 
causes,  and  to  act  accordingly  in  the  handling  and  disposal 
of  the  carcass.  The  slower  process  of  the  acute  and  sub- 
acute types  of  anthrax  and  the  evident  symptoms  give 
greater  opportunity  for  the  recognition  of  the  nature  of  the 
trouble.  The  mortality  from  the  disease  is  from  70  to  80 
per  cent. 

Lesions. — The  lesions  are  usually  so  characteristic  that 
they  enable  the  recognition  of  the  disease^  or  at  least  arouse 
suspicion  as  to  its  probable  cause.  The  most  marked  is 
the  dark  blood,  which  may  appear  almost  tar-like  and  which 
does  not  coagulate  as  does  normal  blood.  The  spleen,  or 
milt,  is  usually  greatly  increased  in  size;  it  is  dark  red  in 
color  instead  of  the  grayish  color  of  the  normal  organ.     The 


ANTHRAX 


257 


258  AGRICULTURAL  BACTERIOLOGY 

interior  has  a  semi-liquid  consistency  due  to  the  breaking 
down  of  its  structure.  Hemorrhages  or  areas  in  which  the 
blood  has  passed  from  the  blood-vessels  into  the  tissues  are 
often  noted  in  the  internal  organs  and  on  the  membranes. 
Blood  often  issues  from  the  natural  openings  of  the  body. 

The  carbuncles  are  at  first  hard,  hot,  and  painful,  but 
later,  due  to  the  death  of  the  tissue  at  the  center,  the  fever 
subsides,  and  no  pain  is  evidenced  by  the  animal  when  the 
carbuncle  is  opened.  The  exudate  is  tarlike  in  color  and 
consistency.  Gangrene,  due  to  a  secondary  invasion  of 
the  abscess  with  putrefactive  bacteria,  is  often  noted.  In 
the  case  of  the  hog,  swelling  of  the  tissues  of  the  throat  is 
commonly  present.  The  carcass  does  not  become  rigid; 
bloating  and  decomposition  occur  more  quickly  than  in  the 
case  of  death  from  other  causes. 

The  sudden  death  of  cattle  or  sheep,  accompanied  by 
black  non -coagulating  blood  and  an  enlarged  darkened 
spleen,  should  always  lead  to  a  suspicion  of  anthrax.  The 
absence  of  these  typical  lesions  is  not  to  be  considered  proof 
of  the  absence  of  anthrax. 

The  disease  is  a  true  septicemia  in  that  the  organisms 
are  to  be  found  in  great  numbers  in  every  portion  of  the 
body  at  the  time  of  death.  The  absolute  diagnosis  of  the 
disease  is  made  by  finding  the  anthrax  bacillus  in  the  tis- 
sues, and,  in  some  cases  in  which  the  post-mortem  changes 
are  not  typical,  this  is  the  only  way  in  which  the  diagnosis 
can  be  made  with  certainty. 

Whenever  an  animal  has  died  and  anthrax  is  suspected, 
the  temperature  of  each  animal  in  the  herd  should  be  taken. 
All  that  show  a  temperature  of  104°  F.  or  above  should 
be  allowed  to  remain  in  the  infected  quarters ;  the  remainder 
of  the  animals  should  be  at  once  removed. 

Before  the  transmissible  nature  of  the  disease  was  rec- 
ognized, extensive  epidemics  were  common.     Prompt  sep- 


ANTHRAX  259 

aration  of  the  animals,  and  care  in  the  disposal  of  the  car- 
cass and  in  disinfetion  will  do  much  to  prevent  continued 
loss.  It  has  been  shown  that  the  loss  of  one  or  two  animals 
from  a  herd  by  anthrax*  is  a  more  common  occurrence  than 
is  a  more  extensive  outbreak.  Carelessness,  however,  may 
result  in  <rreat  losses. 

Vaccination. — The  development  of  a  protective  treatment 
against  anthrax  was  one  of  the  great  gifts  of  Pasteur  to  the 
world.  Starting  from  observations  he  had  made  on  chicken 
cholera,  he  devised  ways  of  attenuating  the  anthrax  organ- 
ism by  growing  it  at  a  temperature  above  its  optimum. 
The  longer  the  organism  was  grown  at  this  unfavorable  tem- 
perature, the  less  virulent  it  became.  The  weakened 
organism  was  unable  to  produce  a  serious  form  of  the  dis- 
ease when  introduced  into  the  tissues  of  a  susceptible  ani- 
mal. It  did,  however,  grow,  and  cause  the  animal  to 
produce  substances  that  protected  it  against  a  natural 
attack  of  the  disease.  The  original  method  of  Pasteur  was 
to  apply  the  vaccine  in  two  doses  at  an  interval  of  ten  days. 
The  vaccines  were  standardized  by  injecting  them  into 
small  animals.  The  first  vaccine  should  possess  such  a  de- 
gree of  virulence  that  it  would  kill  white  mice,  but  not 
guinea-pigs;  the  second  should  kill  the  latter  animal,  but 
not  rabbits.  This  mode  of  treatment  caused  the  loss  of 
about  1  per  cent,  of  the  treated  animals.  It  served  to  re- 
duce the  losses  in  cattle  and  sheep,  especially  in  France,  to 
a  marked  extent.  The  immunity  thus  conferred  is  active  in 
form,  persisting  for  about  one  year. 

It  is  evident  that  difficulties  are  encountered  in  the 
preparation  of  the  vaccine.  If  it  is  weakened  too  much,  it 
will  give  but  a  slight  degree  of  protection.  If,  on  the 
other  hand,  it  is  not  weakened  sufficiently,  the  animals  with 
a  low  degree  of  resistance  will  be  unable  to  withstand  the 
effects  of  the  vaccine  and  will  die.     The  vaccines  also  de-. 


260  AGRICULTURAL  BACTERIOLOGY 

leriorate  rapidly.  Their  use  under  carefully  controlled  con- 
ditions is  successful.  Such  conditions  were  obtained  in 
France  both  as  to  preparation  and  use.  Under  commer- 
cial conditions  in  this  country,  the  Pasteur  type  of  vaccine 
has  not  been  an  unqualified  success. 

Recently  the  simultaneous  application  of  the  protective 
serum  and  vaccine  has  been  introduced.  A  horse  is  immun- 
ized by  the  injection  of  gradually  increasing  doses  of  a 
virulent  culture  of  anthrax.  It  is  possible  so  to  accustom 
the  animal  to  the  organism  that  500  cubic  centimeters  of  a 
highly  virulent  culture  can  be  given  at  one  time,  or  more 
that  ten  thousand  times  as  much  as  would  have  killed  the 
animal  at  first.  The  blood  of  the  horse  will  have  a  high 
content  of  protective  bodies.  The  animal  to  be  protected 
is  injected  with  a  quantity  of  serum  on  one  side  of  the 
body  and  with  a  small  quantity  of  a  somewhat  weakened 
culture  on  the  other.  The  United  States  Bureau  of  Animal 
Industry  has  prepared  a  spore  vaccine  for  use  with  serum. 
The  vaccine  is  very  permanent,  due  to  the  resistance  of  the 
spores.  But  one  treatment  is  necessary,  and,  it  is  claimed, 
no  losses  are  occasioned  by  the  treatment.  The  treatment 
can  be  used  only  on  non-infected  animals.  In  the  vaccina- 
tion of  a  herd  in  which  the  disease  has  appeared,  only  ani- 
mals with  normal  temperatures  should  be  vaccinated.  The 
other  animals  should  receive  only  the  serum,  which  is  a 
curative  as  well  as  a  preventive  agent.  The  stock-owner 
should  not  rely  on  vaccination  alone  to  prevent  the  spread 
of  the  disease,  but  should  use  all  possible  precautions  to 
limit  the  distribution  of  the  organism,  especially  in  the  dis- 
posal of  carcasses. 

Disposal  of  carcasses. — In  the  unopened  carcass  the  or- 
ganism cannot  form  spores,  owing  to  the  lack  of  oxygen; 
but  in  the  discharges  from  the  nose  and  rectum,  and  in  any 
J)lood  that  may  be  brought  in  contact  with  the  air  in  making 


ANTHRAX  261 

a  post-mortem  examination,  spore  formation  readily  oc- 
curs. In  the  vegetative  form  the  organisms  are  easily 
killed;  but  the  spores  are  exceedingly  resistant,  so  that 
every  precaution  should  ])e  taken  to  prevent  the  blood 
from  coming  in  contact  with  the  air.  The  carcass  should 
not  be  skinned  or  opened,  unless  it  is  necessary  for  the  pur- 
pose of  establishing  the  cause  of  death.  If  it  is  not  possible 
to  destroy  the  carcass  at  the  place  where  death  occurred,  it 
should  be  removed  by  placing  it  on  a  stone-boat  instead  of 
dragging  it  on  the  ground.  The  opening  of  the  carcass 
should  take  place  only  at  the  point  where  its  ultimate  dis- 
posal is  to  be  carried  out,  which,  if  possible,  should  be  by 
burning  rather  than  burying.  If  the  carcass  is  buried,  it 
should  be  covered  with  quick-lime  in  a  spot  where  there 
will  be  no  danger  of  the  carcass  being  washed  out.  It  is 
well  to  fence  in  the  spot  to  keep  out  dogs  and  stock.  In 
the  unopened  carcass  the  vegetative  organisms  rapidly  die 
owing  to  putrefactive  processes.  The  great  danger  in  an- 
thrax lies  in  the  non-recognition  of  the  first  case  and  in 
the  careless  disposal  of  the  carcass. 

Anthrax  of  man. — Man  is  less  susceptible  to  anthrax  than 
are  cattle  and  sheep.  In  the  disposal  of  anthrax  cadavers, 
especially  when  the  disease  is  not  recognized  and  the  hide 
is  removed,  there  is  great  danger  of  infection  through 
wounds  on  the  hands  or  those  inflicted  during  the  process 
of  skinning.  In  case  infection  occurs,  the  trouble  is  likely 
to  be  localized  in  the  form  of  a  carbuncle  at  the  point  of 
entry.  In  the  handling  of  infected  material  such  as  hides, 
wool  and  bristles,  the  workers  are  likely  to  become  infected, 
especially  when  the  material  is  handled  in  a  dry  condition, 
so  that  the  spores  of  the  anthrax  bacilli  may  be  taken  into 
the  lungs  or  into  the  alimentary  tract.  Both  respiration 
and  ingestion  anthrax  are  usually  fatal. 

Importance  of  correct  diagnosis. — There  are  a  number 


262  AGRICULTURAL  BACTERIOLOGY 

of  diseases  that  are  frequently  mistaken  for  anthrax,  and, 
since  the  advent  of  vaccines  for  the  prevention  of  some  of 
these  diseases,  it  is  much  more  important  than  formerly 
that  a  correct  diagnosis  be  made.  In  cases  that  show  typ- 
ical lesions  there  is  little  danger  of  confusion;  but  cases 
occur  that  are  more  or  less  atypical,  and  frequently  a  bac- 
teriological examination  of  the  tissues  is  necessary  to  de- 
termine the  cause  of  the  trouble  v^ith  accuracy.  For  this 
purpose  samples  of  the  tissues  must  be  forwarded  to  some 
laboratory  for  examination.  Such  laboratories  are  main- 
tained by  many  States  in  connection  with  the  colleges  of 
agriculture. 

The  tissues  should  be  so  packed  that  they  will  not  be  a 
source  of  danger  to  those  who  must  handle  them  in  trans- 
portation. The  tissue  should  be  placed  in  a  jar  that  is 
closed  so  tightly  that  no  liquid  can  escape.  The  jar  should 
be  packed  in  a  mixture  of  sawdust  and  cracked  ice  and  sent 
at  once  to  the  laboratory.  No  disinfectant  should  be  added 
if  a  bacteriological  examination  is  desired ;  the  putrefactive 
processes  must  be  delayed  as  much  as  possible  by  the  main- 
tenance of  a  low  temperature.  In  order  to  avoid  the  dan- 
gers due  to  the  sending  of  the  moist  tissues,  some  of  the 
blood  may  be  placed  in  a  concave  piece  of  glass,  such  as  a 
fruit- jar  cover,  and  allowed  to  dry. 

Every  animal  that  dies  from  an  unknown  cause  should 
be  subjected  to  a  post-mortem  examination  by  a  competent 
person.  In  making  such  examination,  it  is  well  to  proceed 
on  the  supposition  that  the  cause  of  death  is  due  to  an  or- 
ganism dangerous  to  man.  The  hands  should  be  examined 
for  wounds,  and  in  all  cases  it  is  well  to  coat  the  hands  with 
grease  before  beginning  the  examination.  It  should  also 
be  remembered  that  the  cause  of  the  death  may  be  traceable 
to  something  that  can  be  communicated  to  other  a-nimals  of 
the  herd,  and  the  examination  should  not  be  made  until 


BLACKLEG  263 

the  carcass  has  been  brought  to  the  place  of  final  disposal. 
Such  simple  precautions  may  be  cheap  insurance  against 
future  trouble. 

Blackleg. — A  disease  frequently  mistaken  for  anthrax  is 
that  commonly  called  blackleg  or  symptomatic  anthrax. 
Before  the  causal  organisms  of  the  two  diseases  were  discov- 
ered, it  was  thought  that  blackleg  was  a  special  form  of 
anthrax.  The  disease  is  also  known  under  the  names  quar- 
ter-ill or  quarter-evil.  The  causal  organism  is  called  Bacil- 
lus Chauvei.  It  is  a  large  rod  which  grows  only  under 
anaerobic  conditions.  It  produces  spores  in  the  tissues  of 
the  unopened  animal,  a  property  that  differentiates  it 
sharply  from  the  anthrax  bacillus. 

Blackleg  is  found  in  all  parts  of  the  world,  from  the 
tropical  regions  to  the  northernmost  limits  at  which  cattle 
are  kept.  In  the  United  States  it  is  most  common  in  the 
great  grazing  States  of  the  Southwest.  There  are  infected 
localities  in  many  of  the  States  east  of  the  Mississippi  River. 
The  disease  has  often  been  mistaken  for  poisoning  in  local- 
ities in  which  it  was  not  known  to  occur.  It  has  been 
probably  the  most  important  disease  in  the  great  beef-pro- 
ducing districts  of  this  country.  Recently,  means  of  pre- 
vention have  been  so  effectively  used  that  the  disease  has 
greatly  decreased  in  importance. 

Cattle  between  the  ages  of  six  and  eighteen  months  are 
virtually  the  only  ones  that  are  susceptible  to  the  disease. 
It  represents  one  of  the  few  cases  of  age  immunity  to  a 
disease  noted  in  the  lower  animals. 

A  great  increase  in  blackleg  followed  the  introduction 
of  the  improved  breeds  of  beef  cattle  on  to  the  ranges  of 
the  Southwest.  It  is  believed  that  the  thinner  the  skin, 
the  more  likely  is  the  animal  to  acquire  infection. 

Again,  animals  that  are  gaining  in  flesh  rapidly  and  that 
are  taking  little  exercise  seem  to  be  the  most  susceptible. 


264  AGRICULTURAL  BACTERIOLOGY 

It  is  believed  that  this  increased  susceptibility  is  due  to  the 
accumulation  of  lactic  acid  in  the  tissue.  The  effect  of 
lactic  acid  in  increasing  the  ability  of  the  orfianism  to  pro- 
duce disease  can  be  shown  by  injecting  a  weakened  culture 
that  has  been  treated  with  lactic  acid.  The  mixture  will 
produce  a  fatal  attack,  while  the  weakened  culture  alone 
would  not  harm  the  animal. 

It  is  believed  that  the  organism  does  not  pass  directly 
from  one  animal  to  another  by  contact,  but  that  the  infec- 
tion results  from  a  common  source,  the  soil.  It  is  generally 
conceded  that  the  organism  is  introduced  into  the  system 
through  puncture  w^ounds  caused  by  thorns,  spines,  and 
grass  burs,  and  that  to  take  effect  the  organism  must  pene- 
trate the  subcutaneous  tissue,  a  fact  that  explains  the 
greater  ease  with  which  thin-skinned  animals  become  in- 
fected. It  is  a  disease  primarily  of  the  pasture ;  and  hence 
appears  in  the  Northern  States  only  in  the  summer,  but 
farther  South  it  occurs  during  the  entire  year.  It  affects 
sheep  and  goats  less  frequently  than  cattle. 

Symptoms. — The  symptoms  of  the  disease  are  usually  so 
characteristic  that  there  is  little  likelihood  of  its  l)eing  con- 
founded with  other  causes  of  death.  The  general  symptoms 
are  high  fever  and  loss  of  appetite.  The  mucous  mem- 
branes are  at  first  dark  red,  changing  in  the  course  of  a 
few  hours  to  a  dirty  leaden  or  purplish  color. 

The  tumors,  which  appear  most  commonly  in  the  thigh  or 
shoulder,  are  the  most  characteristic  lesion  of  the  disease. 
They  may  be  present  on  the  neck,  chest,  flank,  or  rump — 
indeed,  on  any  part  of  the  body  except  below  the  knee  or 
hock  joints.  The  tumors  are  at  first  small  and  painful; 
they  increase  rapidly  in  size.  The  lymph-glands  in  the  vi- 
cinity of  the  tumors  become  swollen.  The  tumor  is  cool 
to  the  touch  and  painless  in  the  center.  The  skin  covering 
it  is  dryand  parchment-like.     The  lack  of  sensation  at  the 


BLACKLEG  265 

center  of  the  tumor  is  due  to  the  death  of  the  tissue.  Gas 
is  formed  in  the  tissue  to  such  an  extent  that  the  muscle 
fibers  are  blown  apart.  Pressure  on  the  tumor  causes  the 
gas  to  flow  through  the  spaces  with  a  rustling  sound,  which 
gives  rise  to  the  German  term  for  the  disease,  Raiischhrand. 
No  pain  is  evidenced  by  the  animal  when  the  tumor  is 
opened,  for  the  tissues  at  the  center  are  dead.  The  exudate 
is  dark  in  color,  and  has  an  odor  of  rancid  butter,  due  to  the 
presence  of  butyric  ai-id.  The  exudate  is  frothy  on  account 
of  its  gas  content.  The  dark  color  and  location  of  the  tu- 
mors have  given  rise  to  the  common  name  of  the  disease, 
blackleg. 

The  gas  formation  continues  after  death,  often  greatly 
distending  the  carcass.  The  affected  tissues  do  not  decom- 
pose nearly  so  quickly  as  the  non-affected  areas  of  the  body. 
A  blood-colored  frothy  discharge  flows  from  the  nostrils  and 
anus.  The  blood  is  normal  in  color  and  in  coagulating 
properties.  The  spleen  is  normal.  These  conditions,  to- 
gether with  the  gas  formation  in  the  tumors,  something  lack- 
ing in  anthrax  tumors,  serve  to  differentiate  blackleg  from 
anthrax.  The  disease  is  almost  always  fatal.  Treatment 
is  of  little  if  any  value. 

The  stockman  must  seek  to  limit  the  spread  of  the  disease 
by  hygienic  and  preventive  measures  Care  should  be 
used  in  the  disposal  of  carcasses  in  order  not  to  contaminate 
the  soil  with  the  resistant  spores,  which  are  abundant  in 
the  exudate  and  in  the  diseased  tissue.  Cremation  of  the 
carcass  is  advisable  whenever  possible.  Deep  burial  is  a 
substitute.     There  is  no  danger  of  transmission  to  man. 

Vaccination. — The  vaccination  against  blackleg,  first  used 
in  France,  has  been  of  great  value  to  the  stock  interests  of 
this  country.  Before  the  introduction  of  the  protective 
treatment  in  the  Southwest,  the  losses  amounted  to  10  per 
cent,  of  the  annual  calf  crop.     These  losses  were  reduced 


266  AGRICULTURAL  BACTERIOLOGY 

to  one-half  of  one  per  cent,  by  the  use  of  the  vaccine  dis- 
tributed by  the  Bureau  of  Animal  Industry  of  the  United 
States  Department  of  Agriculture. 

The  vaccine  is  made  by  inoculating  an  animal  with  the 
blackleg  bacillus.  After  death  the  affected  muscular  tissue 
is  removed  and  reduced  to  a  pulp,  which  is  then  squeezed 
through  a  cloth.  The  juice  is  dried  quickly  at  95°  F. 
The  cake  thus  obtained  may  be  stored  for  long  periods, 
since  it  contains  the  resistant  spores  of  the  organism. 

AVhen  it  is  desired  to  prepare  vaccine,  the  dried  mater- 
ial is  mixed  with  water  and  heated  to  from  212°  F.  to  219° 
F.  for  seven  hours.  This  treatment  weakens  the  spores  to 
such  an  extent  that  a  fatal  form  of  the  disease  is  not  pro- 
duced when  a  suspension  of  the  material  obtained  after  heat- 
ing is  injected  into  animals.  But  one  treatment  is  neces- 
sary. The  fact  that  only  animals  between  the  ages  of  six 
and  eighteen  months  are  susceptible  to  blackleg,  and  the  fur- 
ther fact  that  vaccination  will  protect  during  the  suscepti- 
ble period  have  made  the  preventive  treatment  a  great  prac- 
tical success.  More  than  25,000,000  doses  have  been  dis- 
tributed by  the  government  to  stock-raisers. 

Hemorrhagic  septicemia. — Sudden  death  with  no  well 
defined  symptom  is  likely  to  be  ascribed  to  poison  or  light- 
ning. The  next  most  common  cause  to  which  sudden  death 
in  cattle  and  sheep  is  ascribed  is  anthrax.  As  has  been 
pointed  out,  the  use  of  specific  biological  products  in  pre- 
vention necessitates  the  correct  diagnosis  of  the  first  cases 
of  death  in  a  herd,  in  order  that  effective  means  of  control 
may  be  emplo^^ed.  Another  disease,  commonly  known  as 
hemorrhagic  septicemia  from  the  fact  that  the  causal  or- 
ganisms produce  reddened  congested  areas  in  the  tissues,  is 
not  infrequently  confounded  with  the  above  causes  of  death. 

The  organism  causing  the  disease  is  one  of  a  large  group 
producing    a    number    of    diseases    in    different    animals. 


HEMORRHAGIC  SEPTICEMIA  267 

Among  the  most  important  are  chicken  cholera,  swine 
plague,  and  bubonic  or  Asiatic  plague  in  man.  In  cattle, 
deer,  and  related  animals,  outbreaks  of  varying  intensity  oc- 
cur. The  disease  is  found  in  all  parts  of  the  world.  In 
the  United  States  it  has  been  most  frequent  in  the  upper 
Mississippi  Valley.  The  discussion  in  question  will  be  lim- 
ited to  the  disease  in  cattle. 

The  normal  habitat  of  the  organism  is  unknown.  It 
has  been  thought  by  some  to  be  a  saprophytic  organism,' 
which,  under  unknown  conditions,  may  suddenly  become 
virulent,  and  thus  cause  an  epidemic  that  usually  disappears 
as  quickly  and  as  mysteriously  as  it  appears.  The  rapidity 
of  its  appearance  and  the  suddenness  with  which  the  animals 
die,  together  with  the  helplessness  of  the  owner  to  combat  it, 
make  it  a  disease  much  to  be  dreaded.  Frequently  the  an- 
imals die  without  showing  previous  symptoms  of  illness. 
In  less  acute  types  of  the  disease,  weakness  of  the  limbs  may 
be  noted.     Recovery  is  rare. 

The  manner  in  which  the  organism  enters  the  body  is 
unknown,  as  is  also  the  method  of  transmission  from  one 
animal  to  another. 

On  post-mortem  examination  reddish  spots  varying  from 
a  pinhead  to  several  inches  in  diameter  are  found  beneath 
the  skin.  Hemorrhagic  areas  are  usually  present  on  the 
heart)  stomach,  and  intestines.  The  blood  is  red  and  coag- 
ulates *in  a  normal  manner.  The  spleen  is  normal.  It  is 
frequently  mistaken  for  anthrax  on  account  of  the  sudden- 
ness with  which  death  occurs.  In  atypical  cases  an  examin- 
ation of  the  blood  for  the  specific  organism  is  necessary  to 
confirm  the  diagnosis. 

A  method  of  vaccination  has  been  devised.  The  causal 
organism  is  g  oviji  in  broth.  The  cultures  are  heated  to 
55°  C.  (131°  F.)  for  thirty-  minutes  in  order  to  destroy 
the  life  of  the  cells.     The  low  degree  of  heat  does  not  change 


268  AGRICULTURAL  BACTERIOLOGY 

them  chemically  to  such  an  extent  that  they  are  unable 
to  stimulate  the  vaccinated  animal  to  produce  bodies 
that  protect  from  a  natural  attack.  The  term  ''bac- 
terine"  is  applied  to  killed  cultures  of  bacteria  used  for 
protective  purposes.  The  vaccine  used  to  protect  against 
typhoid  fever  is  of  this  nature.  The  value  of  the  vaccine 
in  preventing  hemorrhagic  septicemia  is  not  fully  estab- 
lished. In  small  herds  the  isolation  of  the  healthy  animals 
from  those  that  show  any  symptoms  is  preferable  to  vac- 
cination. The  healthy  animals  should  be  removed  to  a 
fresh  pasture  or  meadow  and  staked  out  so  that  no  contact 
between  the  animals  can  take  place.  The  carcasses  should 
be  disposed  of  with  the  same  care  as  in  the  case  of  anthrax. 
If  animals  die  in  the  stable,  the  litter  should  be  burned, 
the  stable  cleaned  and  disinfected.  The  organisms  are 
easily  destroyed,  since  they  do  not  form  spores;  conse- 
quently there  is  no  danger  that  they  will  persist  in  yards 
and  stables,  as  in  the  case  of  anthrax. 

Corn-stalk  disease. — In  those  sections  of  the  country  in 
which  it  is  the  custom  to  harvest  the  ear  corn  in  the  row, 
and  then  turn  the  stock  into  the  standing  fodder,  a  disease 
known  as  corn-stalk  disease  is  sometimes  encountered.  The 
trouble  appears  soon  after  the  cattle  or  horses  are  turned 
into  the  field  (four  to  ten  days)  and  runs  a  rapid  course. 

On  account  of  the  suddenness  with  which  death  occurs, 
and  the  large  losses  that  follow  in  a  short  time,  it  is  often 
mistaken  for  a  contagious  disease,  especially  for  anthrax, 
blackleg,  or  hemorrhagic  septicemia.  It  is  important,  how- 
ever, to  differentiate  the  trouble,  which  is  probably  phys- 
iological, from  those  diseases  that  are  caused  by  specific 
organisms.  The  differentiation  can  be  made  by  the  lack 
of  abnormal  changes  in  the  tissues,  and  the  relation  of  the 
appearance  of  the  disease  to  the  period  of  admission  of  the 
animals  to  the  fields. 


CHAPTER  XXI 
TUBERCULOSIS 

Tuberculosis  is  one  of  the  most  important  communicable 
diseases  of  both  man  and  domestic  animals.  In  the  latter 
it  is  of  both  economic  and  sanitary  importance,  since,  as 
noted  in  the  spread  of  diseases  by  means  of  foods,  a  portion 
of  the  tuberculosis  occurring  in  man  is  due  to  the  organism 
from  bovine  sources.  Statistics  show  that  one  seventh  of 
all  deaths  of  human  beings  are  due  to  tuberculosis,  and 
that  one  third  of  the  mortality  occurring  between  the  ages 
of  twenty  and  forty-five,  the  productive  period  of  life,  is 
caused  by  the  tubercle  bacillus. 

Animals  affected. — All  of  the  domestic  animals  may  be 
affected,  but  the  disease  is  most  prevalent  among  cattle, 
hogs  and  fowls.  The  otlfer  domestic  animals  are  rarely  af- 
fected. Besides  the  domestic  animals,  a  large  number  of 
wild  animals  are  also  susceptible.  There  is  probably  little 
or  no  opportunity  for  wild  animals  to  come  in  contact  with 
the  organism  in  nature,  but  when  placed  in  captivity  where 
there  is  opportunity  for  infection,  the  disease  makes  rapid 
strides.  It  is  the  chief  cause  of  death  of  monkeys,  caged 
animals,  and  birds  in  zoological  gardens.  In  the  London 
zoological  garden  30  per  cent,  of  the  birds  that  died  were 
found  to  have  tuberculosis.  A  disease  caused  by  an  organ- 
ism belonging  to  the  same  group  as  the  tubercle  bacillus 
produces  what  has  been  termed  tuberculosis  in  some  of  the 
cold-blooded  animals. 

Distribution. — Within  very  recent  times  the  commerce 
in  domestic  animals  and  their  products  and  in  cultivated 

269 


270  AGRICULTURAL  BACTERIOLOGY 

plants  has  increased  in  a  most  remarkable  manner,  due  to 
the  development  of  methods  of  transportation.  From  north- 
western Europe  the  improved  breeds  of  cattle,  sheep, 
horses,  and  hogs  have  been  shipped  to  all  parts  of  the 
world,  and  with-  them  have  been  carried  the  diseases  with 
which  they  were  affected.  Many  countries  into  which  such 
diseases  were  thus  introduced  had  been  previously  free 
from  them,  and  could  have  been  kept  so  if  there  had  been 
sufficient  knowledge  concerning  the  nature  of  these  com- 
municable diseases,  their  detection  and  mode  of  dissemina- 
tion. This  knowledge,  in  many  instances,  was  acquired 
only  after  the  harm  had  been  done.  The  United  States  is 
still  free  from  some  of  the  communicable  diseases  that  are 
a  cause  of  great  loss  to  the  farmers  of  Europe,  and  it  be- 
hooves us  to  use  all  possible  precautions  to  prevent  their 
introduction  into  this  country. 

The  islands  of  Jersey  and  Guernsey  are  the  only  impor- 
tant breeding  centers  that  are  free  from  tuberculosis,  and 
this  condition  has  resulted  from  a  rigidly  enforced  rule  that 
no  live  cattle  should  be  imported  on  to  these  islands.  The 
percentage  of  animals  affected  with  the  disease  ranges  from 
over  50  in  some  of  the  German  states,  as  Satxony,  to  less 
than  5  in  our  Western  and  Southern  States.  The  disease 
is  not  widespread  in  those  sections  in  which  cattle-raising 
is  not  important  and  into  which  the  improved  breeds  have 
not  been  introduced  in  considerable  numbers.  In  England 
it  is  asserted  that  less  than  5  per  cent,  of  the  milking  herds 
of  Shorthorn,  Ayrshire,  and  Jersey  cattle  are  free  from 
tuberculosis,  while  in  Wisconsin,  one  of  the  most  impor- 
tant dairy  States  in  this  country,  not  over  one  third  of  the 
herds  contain  any  tubercular  animals.  In  the  Eastern 
States,  in  which  dairying  has  been  longer  established,  the 
percentage  of  affected  herds  is  higher. 

The  rapid  spread  of  the  disease  within  recent  years  is 


TUBERCULOSIS 


271 


shown  in  the  following  figures,  which  indicate  the  percent- 
age of  animals  found  to  be  tubercular  on  slaughter. 


Cattle 

% 

Calves 

% 

Sheep 

Hogs 

% 

Horses 

% 

Bavaria    

1898 
1900 

1808 
1906 

1898 
1906 

5.07 
10.31 

16.09 
23 .  40 

30.46 
37.58 

0.05 
0.28 

0.15 
0.33 

0.24 
0.50 

0.12 

0.11 
0.17 

0.09 
0.09 

0.35 
1.40 

2.32 
2.96 

3.16 
5.07 

0.11 

Prussia    

0.12 
0.16 

Saxonv                 .... 

0.16 
0.30 

The  only  figures  available  as  to  the  spread  of  the  disease 
in  this  country  are  those  collected  by  the  Bureau  of  Animal 
Industry  in  the  meat  inspection  service  which  is  maintained 
in  all  the  larger  packing-houses  of  the  country.  The  fol- 
lowing table  presents  the  data  with  reference  to  the  per- 
centage of  animals  found  tubercular  on  post-mortem  ex- 
amination. 

Cattle  Swine 

%  % 

1907  0.4  1.5 

1908  0.9  2.0 

1909  1.3  2.4 

1910  1.5  '2.7 

1911  1.7  3.7 

1912  2.1  4.6 

1913  2.1  5.6 

1914  2.1  6.6 

1915  2.3  7.6 

1916  2.6  7.2 

1917  2.3  9.8 

1918  2.0  7.0 

These  figures  show  that  tuberculosis  has  increased  in 
this  country  rapidly  in  recent  years. 

The  disease  is  most  common  in  the  pure  bred  herds — not 


272  AGRICULTURAL  BACTERIOLOGY 

because  these  animals  are  more  susceptible  than  grades,  but 
because  the  opportunity  for  infection  in  pure  bred  herds 
has  been  much  greater  because  of  the  interchange  through 
purchase.  For  the  same  reason,  large  herds  are  more  likely 
to  be  tubercular  than  small  herds.  The  disease  is  one  that 
spreads  by  direct  contact  among  cattle  kept  out  of  doors 
almost  as  rapidly  as  in  the  case  of  those  that  are  stabled 
for  a  large  part  of  the  year. 

Different  names  are  applied  to  the  various  manifesta- 
tions of  the  disease  in  man.  Consumption  and  phthisis 
refer  to  tuberculosis  of  the  lungs ;  scrofula  to  tuberculosis 
of  the  glands  of  the  neck ;  lupus  to  that  of  the  skin ;  and 
jo':nt  disease  to  that  of  the  joints.  In  cattle,  grapes  and 
pearl  disease,  terms  sometimes  used  by  butchers,  refer  to 
tuberculosis  of  the  serous  membranes. 

The  tubercle  bacillus. — The  tubercle  bacillus  is  a  slender 
rod  that  is  a  member  of  the  acid-fast  group,  which  includes 
the  organism  causing  leprosy  and  that  producing  Johne's 
disease  in  cattle,  and  also  a  number  of  non-pathogenic  ba- 
cilli, which  are  found  in  manure  and  on  plants.  The  term 
acid-fast  refers  to  the  fact  that  the  organism,  when  stained, 
retains  the  dye  when  treated  with  dilute  solutions  of  min- 
eral acids,  while  other  bacteria  are  decolorized  at  once. 
This  property  of  the  tubercle  bacillus  is  used  for  its  detec- 
tion in  sputum,  milk,  and  tissues. 

The  tubercle  bacillus  does  not  produce  spores.  It  is, 
however,  resistant  to  desiccation  and  other  physical  and 
chemical  factors,  a  fact  of  importance  in  the  spread  of  the 
disease.  It  grows  very  slowly  on  all  kinds  of  culture  media, 
and  probably  in  the  animal  body,  a  fact  of  significance  in 
explaining  the  extended  period  of  incubation  of  the  disease, 
which  is  from  a  few  weeks  to  several  months  in  length.  In 
cultures  the  tubercle  bacillus  grows  only  on  the  surface  of 
the  medium. 


TUBERCULOSIS  273 

Infection. — The  organisms  enter  the  body  through  either 
the  respiratory  or  the  alimentary  tract.  The  importance 
of  these  portals  of  entrance  varies  in  different  animals.  It 
is  probable  that  the  bovine  becomes  easily  infected  in  either 
of  these  ways,  while  in  the  case  of  the  hog  the  infection 
under  natural  conditions  is  by  way  of  the  alimentary  tract. 
The  guinea-pig,  one  of  the  most  susceptible  animals,  ac- 
(luires  the  disease  with  ease  by  the  inhalation  of  the  bacilli, 
while  it  is  very  resistant  to  infection  through  the  alimentary 
tract. 

Lesions. — The  lymph-glands,  which  are  widely  distrib- 
uted in  the  body,  are  to  be  looked  upon  as  filters,  and  tend 
to  remove  any  foreign  solid  particles,  such  as  tubercle  ba- 
cilli, that  have  entered  the  lymph  or  blood  circulation.  The 
bacilli  are  most  likely  to  lodge  in  those  glands  that  are  in 
close  proximity  to  the  point  of  invasion.  Thus,  the  neck 
glands  are  most  frequently  diseased  in  the  hog,  and  the 
glands  near  the  lungs  and  intestines  in  the  bovine.  The 
lungs,  liver,  and  spleen  are  also  frequently  tubercular. 
The  organs  mentioned  are  those  to  which  the  greatest  at- 
tention should  be  paid  in  making  a  post-mortem  examina- 
tion. Any  organ  may  be  tubercular,  such  as  the  heart, 
brain,  udder,  and  neighboring  lymph-glands,  the  joints, 
hones,  and  infrequently  the  lymph-glands  located  in  the 
Huiscles. 

The  bacilli  collect  in  some  of  these  organs  and  grow 
slowly.  Their  by-products  exert  a  stimulus  on  the  body 
cells  in  the  immediate  vicinity,  causing  the  formation  of  the 
characteristic  tubercles  or  nodules.  The  tubercle  is  most 
evident  when  located  on  one  of  the  smooth  serous  mem- 
branes of  the  body,  producing  that  type  of  disease  known 
as  pearl  disease  or  grapes.  The  cells  at  the  center  of  the 
tubercle  are  soon  killed  by  th^  poison  elaborated  by  the 
bacilli.     As  the  area  of  the  dead  tissues  continues  to  in- 


274 


AGRICULTURAL  BACTERIOLOGY 


crease,  the  tubercles  may  bc-^ome  confluent,  and  form  tu- 
bercular abscesses  of  varying  sizes.     Ultimately  these  ab- 


Fig.  43.     Tubercular  Omentum 

In    a    healthy    animal   this    is    a    smooth    thin    membrane.      Grapes    is    the    term 

commonly   applied    to   this   form    of   disease   by    the    butcher 

scesses  break  and  discharge  their  contents  into  the  air- 
passages  of  the  lungs,  the  milk-ducts,  the  bile-ducts,  or 
into  some  other  opening  that  will  enable  the  bacilli  to  escape 
from  the  body.  This  condition  is  known  as  "open"  tuber- 
culosis, as  opposed  to  the  ' '  closed ' '  form  where  the  tubercles 
do  not  break  down. 

The  tubercular  animal  is  a  source  of  danger  to  others 
only  as  it  is  eliminating  the  organisms  from  the  body.  If 
the  disease  has  not  reached  the  open  stage,  or  if  the  lesions 
are  found  in  parts  of  the  body  that  have  no  exterior  open- 
ing, the  animal  can  not  be  dangerous  to  others  or  to  the 
human   beings   consuming  the   milk.     It   is   impossible   to 


TUBERCULOSIS  275 

foretell  wlien  the  closed  form  of  the  disease  will  change  to 
the  open,  as  it  is  certain  to  do  if  the  disease  progresses. 
Hence  every  affected  animal  must  be  considered  a  potential 
source  of  danger  to  the  herd  and  to  public  health. 

The  tubercles  vary  in  size  from  a  pinhead  to  abscesses  as 


Fig.  44.     A  Tubercular  Spleen 

Tliis  organ  shows  a  number  of  tubercles.      It   is  an  t'.\aniplo  of  tuberculosis  in 

hogs  due  to  the  feeding  of  infected  milk 

large  as  the  closed  fist.  The  small  tubercles  are  usually  of 
a  light  pearly  gray  color  throughout,  or  they  may  show  a 
yellowish  area  at  the  center,  composed  of  dead  tissue.  The 
larger  tubercles  and  abscesses  may  be  filled  with  creamy 
pus,  or  with  hard,  gritty  yellow  material  due  to  the  depo- 
sition of  lime  salts.  The  tubercle  is  then  said  to  be  calci- 
fied, and  its  contents  have  the  appearance  of  corn  meal. 

The  lungs  of  a  healthy  animal  are  light  pink  in  color  and 
spongy  in  texture;  in  the  tubercular  organ  the  firm,  hard 
tubercles  may  be  felt  upon  pressure,  or  they  may  even  be 
raised  above  the  surface  of  the  lung.  As  has  been  stated, 
the  disease  is  readily  recognized  in  the  liver  and  spleen 
by  the  sharp  contrast  between  the  yellow  affected  areas  and 
the  surrounding  healthy  tissue. 

Tubercular  organs  and  glands  are  usually  increased  in 
size  in  comparison  with  the  healthy  tissue.  In  the  case  of 
a  tubercular  udder  the  disease  is  usually  confined  to  a  single 
quarter   and   the   affected   part    may   be   much   enlarged. 


276  AGRICULTURAL  BACTERIOLOGY 

There  is  no  fever  or  pain  in  the  tubercular  udder,  as  in  the 
ease  of  acute  inflammations. 

Distribution  of  the  tubercle  bacillus. — The  organisms  are 
eliminated  in  the  sputum  discharged  from  the  mouth  in 
the  act  of  coughing,  in  the  feces,  and  to  some  extent  in  the 
milk.  In  the  stable  the  material  from  the  digestive  tract 
becomes  dry,  and  the  dust  therefrom  with  the  adherent  tu- 
bercle bacilli  may  be  drawn  into  the  air-passages  of  healthy 
animals.  The  fodder  or  water  may  be  contaminated  with 
infectious  material,  or  the  transmission  of  the  organism 
may  be  direct,  through  the  diseased  animal  licking  herself 
and  then  being  licked  by  a  healthy  animal.  The  milk  be- 
comes infected  through  the  introduction  of  manure  and 
dust,  and  also  from  tubercular  udders.  The  feeding  of 
such  milk  to  calves  and  hogs  readily  serves  to  infect  them. 
Hogs  also  acquire  the  disease  from  following  cattle  in  the 
feed  lot  or  from  manure.  The  reproductive  organs  are 
rarely  diseased,  and  calves  from  tubercular  dams  ^re  usually 
healthy. 

The  spread  of  the  disease  in  the  herd  may  be  rapid  or 
slow,  the  determining  factor  being  the  prevalence  of  cases 
of  open  tuberculosis.  It  is  a  popular  view  that  the  disease 
will  not  spread  among  cattle  kept  out  of  doors  or  in  stables 
well  ventilated  and  lighted.  Experience  shows  these  views 
to  be  wrong,  and  that  when  open  cases,  or  spreaders,  as  they 
are  called,  which  give  out  large  numbers  of  the  organisms, 
are  present,  the  disease  will  spread  rapidly  under  condi- 
tions ideal  in  other  respects. 

Infection  of  the  herd. — The  infection  of  the  herd  takes 
place  through  the  introduction  of  a  tubercular  animal,  or 
through  the  use  of  contaminated  products,  such  as  the  milk. 
In  the  more  acute  communicable  diseases,  the  transmission 
of  the  organism  from  place  to  place  may  be  accomplished  by 
the  transportation  of  contaminated  objects,  but  in  the  case 


TUBERCULOSIS 


277 


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Fig.  4.").  lUiying  Tuberculosis 
Tlje  bounded  area  in  the  center  of  the  diagram  represents  a  herd  that  was 
dispersed  by  auction  sale.  Dots  signify  tubercular  animals  and  half  black 
cinles  healthy  animals.  The  healthy  animals  in  the  herds  into  which  the 
dispersed  animals  went  are  shown  by  circles.  The  crossed  circles  indicate 
originally  tubercular  animals  in   these  herds.     Note  the  number  of   herds  that 

were   infected   from   the  one   herd 

of  tuberculosis  it  is  certain  that  this  is  of  no  importance, 
and  attention  should  be  focused  on  the  animals  purchased 
and  the  dairy  products  fed.  The  introduction  of  the  dis- 
ease in  the  latter  manner  is  easily  guarded  against  by  re- 
quiring that  the  by-products  of  creameries  and  cheese  fac- 
tories be  properly  heated  before  being  returned  to  the  farm. 
The  rapid  introduction  of  the  farm-separator  has  resulted 
in  the  practical  abolition  of  the  whole  milk  creamery,  and 
this  is  solving  the  problem  of  the  spread  of  tuberculosis  by 
mixed  skim  milk.  The  return  to  the  farms  of  unheated 
whey  is  certainly  an  important  factor  in  the  spread  of  tu- 
berculosis and  other  milk-borne  diseases  of  animals.  New 
York,  Wisconsin,  and  some  other  States  require  the  heating 
of  all  creamery  and  cheese  factory  by-products  before  they 
are  returned  to  the  farms.     Both  farmers  and  operators 


278 


AGRICULTURAL  BACTERIOLOGY 


Fig.  4G.  Tuberculosis  Spread  by  Creamery  Byproducts 
The  tubercular  animals  are  represented  by  dots,  healthy  animals  by  circles.  In 
the  two  bounded  areas  thirty  per  cent,  of  the  cattle  were  diseased.  Outside 
of  these  districts  but  five  per  cent,  were  tubercular.  The  feeding  of  mixed 
creamery  skim  milk  was  the  principal  cause  of  the  conditions  Avithin  the 
bounded  areas 


TUBERCULOSIS  279 

should  welcome  such  a  regulation,  for  the  effect  of  its  eu- 
forceraeiU  is  to  prevent  the  spread  of  disease  and  to  im- 
prove the  quality  of  milk  supplied  by  the  farmer  to  the 
operator. 

The  prevention  of  the  introduction  of  incipiently  dis- 
eased animals  into  the  herd  is  a  far  mor*e  difficult  problem. 
The  history  of  the  disease  in  the  individual  animal  usually 
shows  a  slow  but  not  a  continually  progressive  development. 
Periods  of  development  are  followed  by  periods  of  dor- 
mancy, in  which  neither  the  animal  nor  the  parasite  is 
active  in  its  attack  on  the  other.  The  organisms  remain 
alive  in  the  tissues,  and  during  periods  of  diminished  vital- 
ity in  the  animal  may  find  opportunity  for  renewed  action, 
causing  a  rapid  progress  of  the  disease.  In  man  recovery 
from  infection  is  the  rule  rather  than  the  exception,  while 
in  cattle  recovery  is  probably  so  rare  that  it  can  not  be 
considered  as  a  factor  in  the  fi^ht  against  the  disease.  For- 
tunately, the  period  of  latency  may  cover  several  years,  and 
so  permit  of  its  detection  in  the  earlier  stages  of  the  disease 
before  the  infected  animal  becomes  an  element  of  danger. 

Detection  of  tuberculosis. — In  the  early  stages  of  the  dis- 
ease it  is  impossible  to  detect  it  by  a  physical  examination 
alone.  Not  until  the  disease  has  made  sufficient  progress  to 
affect  in  considerable  degree  the  general  health  of  the  ani- 
mal are  the  symptoms  apparent,  even  to  an  experienced 
person.  In  the  last  stages  the  animal  becomes  emaciated., 
the  hair  rough,  the  eyes  sunken,  and  the  head  often  ex- 
tended. The  appetite  may  remain  good,  but  food  seems  to 
have  no  effect.  If  the  lungs  are  involved,  coughing  may  be 
noted,  especially  after  the  animal  has  been  forced  to  violent 
exercise.  In  the  case  of  glands  that  can  be  examined  in 
the  living  animal,  such  as  those  of  the  neck  and  udder,  an 
enlarged  condition  should  always  arouse  suspicion.  It  is 
impossible  for  the  average  farmer  or  veterinarian  to  tell 


280 


AGRICULTURAL  BACTERIOLOGY 


A  Tubercular  Animal 


The    animal    showed    no    physical    symptoms    although    it    was    eliminating    the 
disease-producing  organisms  and   was  thus  serving  to  infect  the  remainder  of 

the   herd 


from  a  physical  examination  alone  whether  an  animal  has 
tuberculosis  or  not,  or  to  determine  the  stage  of  the  disease. 
An  animal  may  be  apparently  in  perfect  health,  and  yet  be 
dangerous  to  other  animals  because  of  the  elimination  of 
tubercle  bacilli. 

Many  of  the  open  cases  can  be  detected  on  physical  exami- 
nation by  veterinarians  highly  trained  in  physical  diagnosis, 
especially  when  aided  b}^  a  microscopic  examination  of  the 
excretions.  The  physical  diagnosis  and  detection  of  the 
open  cases  form  the  basis  of  the  Ostertag  method  of  elimi- 
nating the  disease,  as  practised  in  Germany.  This  is  ap- 
plied especially  where  the  percentage. of  diseased  animals 
is  so  high  that  the  removal  of  the  tubercular  animals  be- 
comes an  economic  impossibility.     The  method  has  not  been 


TUBERCULOSIS 


281 


used  for  a  long  enough  period  to  give  indications  as  to  its 
final  success.  In  many  sections  of  the  United  States  it 
would  not  place  an  impossible  burden  on  the  dairy  industry 
if  all  tubercular  animals  were  removed  from  the  herds.  In 
order  to  detect  the  disease  in  the  herd,  and  to  determine 


Fig.  48.  A  Tubercular  Animal 
An  advanced  case  of  tuberculosis.     Such  an  animal  is  termed  a 

"canner" 


piner 


the  real  condition  of  animals  to  be  introduced  into  the  herd, 
a  more  effective  method  of  detecting  the  disease  than  physi- 
cal diagnosis  must  be  employed. 

The  diagnosis  of  the  disease  can  be  made  with  the  greatest 
certainty  by  applying  what  is  known  as  the  tuberculin  test. 
Tuberculin  was  originally  devised  by  Robert  Koch  as  a  cure 
for  tuberculosis.  Its  use  in  the  case  of  cattle  is  of  much 
value  in  indicating  whether  they  are  affected  in  any  degree 
with  the  tubercle  bacillus.  If  any  tubercular  tissue  exists, 
the  introduction  of  tuberculin  causes  a  rise  of  temperature 


282  AGRICULTURAL  BACTERIOLOGY 

which  can  be  easily  determined  by  thermometer  readings 
before  and  after  the  subcutaneous  injection  of  the  tuber- 
culin. 

In  making  tuberculin,  the  tubercle  bacillus  is  grown  in 
beef  broth  to  which  glycerine  has  been  added.  After  the 
maximum  growth  has  been  obtained  the  cultures  are  heated 
to  kill  the  bacilli  and  extract  all  of  their  soluble  cell  prod- 
ucts. This  extract  is  concentrated  to  a  definite  volume,  and 
then  filtered  through  porcelain  filters  to  remove  all  the  dead 
organisms.  It  is,  of  course,  impossible  for  the  tuberculin 
to  produce  tuberculosis,  as  has  often  been  stated  by  those 
ignorant  of  its  nature.  When  this  material  is  brought  in 
contact  with  the  tissues  of  a  healthy  animal,  no  effect  is  to 
be  noted,  while  in  the  case  of  a  tubercular  animal,  an  effect 
varying  with  the  method  of  application  is  produced,  because 
the  tissues  of  the  diseased  animal  are  supersensitive  to  the 
tuberculin. 

There  are  at  present  three  methods  of  applying  tubercu- 
lin :  to  the  eye,  when  it  is  known  as  the  ophthalmic  test ; 
into  the  skin,  when  it  is  called  the  intradermal  test;  anji 
beneath  the  skin,  as  it  was  originally  used,  when  it  is  re- 
ferred to  as  the  subcutaneous  or  thermal  test.  In  the 
former  a  drop  of  tuberculin  is  placed  on  the  eyeball.  A 
more  or  less  marked  inflammation  results  in  a  few  hours  in 
the  case  of  a  tubercular  animal.  If  the  tuberculin  is  intro- 
duced between  the  layers  of  the  skin,  a  swelling  results 
which  is  more  extensive  and  persists  for  a  longer  period 
in  a  tubercular  than  in  a  healthy  animal.  The  subcutane- 
ous test  is  the  more  reliable  and  used  far  more  extensively 
than  the  others,  although  it  takes  a  considerably  longer  time 
to  produce  the  desired  reaction.  In  addition  to  the  tem- 
porary fever  produced  in  a  reacting  animal  by  the  sub- 
cutaneous injection  of  tuberculin,  a  constitutional  reaction 
is  frequently  noted,  as  is  indicated  by  loss  of  appetite,  in- 


TUBERCULOSIS 


283 


creased  respiration,  diarrhea,  and  a  local  swelling  at  the 
point  of  injection.  The  tliermal  reaction  is,  however,  most 
constant,  and  since  it  is  easily  detected  by  taking  the  tern- 


Fig.  49.    Injecting?  Tuberculin 

The  diagnostic  agent  is  injected  beneath  the  skin  of  the  neck  or  shoulder 

perature,  it  is  the  characteristic  on  which  the  greatest  reli- 
ance is  placed. 

Details  of  the  tuberculin  test. — In  testing  an  animal,  a 
series  of  temperatures  should  be  taken  before  the  tuberculin 
is  injected,  to  determine  the  normal  range,  and  to  note  espe- 
cially whether  any  abnormal  condition  obtains.  The  tem- 
perature is  taken  b}^  means  of  a  clinical  thermometer  in- 
serted in  the  rectum.     The  temperature  of  the  bovine  varies 


284 


AGRICULTURAL  BACTERIOLOGY 


considerably  in  different  animals,  and  even  in  the  same 
animal  at  different  times  of  the  day.  The  temperature  of 
healthy  milch-cows  may  range  from  100°  F.  to  over  102°  F. 
The  temperature  of  calves  and  fat  stock  is  usually  higher, 
while  that  of  aged  or  weak  animals  is  lower.  The  vari- 
ations that  may  be  noted  in  a  well  kept,  healthy  animal  are 
illustrated  in  the  following  table,  in  which  are  also  given 
the  pulse  and  number  of  respirations  a  minute.  Exercise, 
excitement,  and  hot  weather  tend  to  increase  the  tempera- 
ture. The  drinking  of  large  quantities  of  cold  water  lowers 
the  temperature  for  some  hours. 


Temperature,  Rate  of  Pulse 

,  and  Respirations  per  Minute 

Cow  No.   1 

Cow  No.  2 

Tem- 
perature 

Pulse 

Resp. 

Tem- 
perature 

P.lse 

Resp. 

10  A.  M... 
12  M 

2    P.    M... 

4    p.    M... 

6    P.    M... 

8  P.  M... 
10  P.  M... 
12    P.    M... 

2    A.    M... 

4    A.    M... 

6    A.    M... 

8    A,    M... 

99.5°  r. 
100.8 
101.6 
103.0 
103.1 
103 
102 
102.5 
102.4 
102.2 
101.8. 
102.5 

66 
54 
48 
66 
57 
56 
60 
56 
64 
54 
60 
56 

18 
15 
15 
24 
18 
16 
20 
16 
18 
24 
18 
16 

98.6°  F. 

99.4 
100.2 
102.7 
103.0 
102.0 
102.0 
101.6 
102.2 
101.5 
102.2 
103.2 

60 
54 
54 
72 
60 
60 
50 
54 
58 
60 
60 
60 

15 
15 

18 
24 
27 
14 
18 
20 
18 
24 
20 
18 

The  temperature  should  be  taken  four  times  at  two-hour 
intervals  before  the  injection  of  the  tuberculin.  The  in- 
jection is  made  by  means  of  a  hypodermic  syringe,  usually 
just  back  or  in  front  of  the  shoulder.  It  may  be  injected 
wherever  the  skin  is  thin  and  loose.  The  needle  is  inserted 
through  a  fold  in  the  skin.  Care  should  be  taken  in  in- 
serting the  needle  to  see  that  it  penetrates  through  the  skin 


TUBERCULOSIS 


285 


but  not  into  the  deeper  lying  muscular  tissue.  Before  the 
syringe  is  used  it  should  be  sterilized  by  placing  it  in  cold 
water  and  bringing  the  water  to  the  boilini^-point. 

The  dose  of  tuberculin  varies,  depending  on  the  degree  of 
concentration.  The  usual  strength  employed  requires  2 
cubic  centimeters  to  1,000  pounds  live  weight.  It  is  desir- 
able that  the  animals  tested  shall  be  in  a  normal  condition; 
hence,  the  injection  of  the  tuberculin  should  be  preceded 


Hours    After 

Injection. 

F 

8 

10 

12 

)4 

16 

16 

20 

107° 

^^^ 

"-v^ 

10  6° 

--^"\ 

/ 

^^ 

-^^ 



10  5° 

/ 

^ 

/x 

^      1 

.^ 

10  4° 

3/X 

^ 

/^2 

10  3° 

y 

102° 

w 

10  1° 

^'==' 

10  0° 

. 

Fig.  50.     Reaction  Curves  in  the  Tuberculin  Test 

Curve  1  represents  the  temperature  of  a  healthy  animal  after  the  injection  of 

tuberculin.     Curves  2  and  3  represent  the  temperatures  of  tubercular  animals 

following   the    administration    of   tuberculin 

by  a  careful  examination  of  each  animal.  Any  animals 
showing  abnormal  temperatures  should  not  be  injected. 
The  normal  physiological  functions,  such  as  calving,  oestrum, 
or  **heat,"  may  or  may  not  affect  the  temperature.  Com- 
plete notes  should  be  made  as  to  the  condition  of  the  ani- 
mals, so  that  these  facts  may  be  considered  in  the  interpre- 
tation of  the  records.  A  negative  reaction  in  the  case  of  a 
cow  in  heat  or  that  has  recently  calved  is  as  reliable  as  on 
any  animal,  while  a  positive  reaction  may  not  be  so  reliable. 
Since  it  takes  a  number  of  hours  to  produce  the  febrile 
reaction  in  the  case  of  an  affected  animal,  it  is  not  neces- 


286  AGRICULTURAL  BACTERIOLOGY 

sary  to  take  temperatures  until  eight  to  ten  hours  after  the 
injection  of  the  tuberculin.  On  account  of  the  length  of 
this  period,  it  is  most  convenient  to  inject  the  tuberculin  in 
the  evening.  Four  or  five  temperature  readings  should  be 
taken  at  two-hour  intervals  until  there  is  a  marked  and 
permanent  decline  toward  the  normal.  In  the  case  of  a 
positive  reaction,  the  temperature  usually  begins  to  rise 
from  10  to  14  hours  after  injection,  reaches  a  maximum 
in  from  12  to  16  hours,  and  then  declines  rapidly.  The 
maximum  temperature  may  reach  from  105°  to  107°  F.,  or 
three  to  five  degrees  above  the  average  normal  temperature. 
The  reaction  is  considered  positive  when  the  highest  tem- 
perature after  the  injection  is  at  least  two  degrees  above  the 
average  normal  before  injection,  or  is  one  and  five  tenths 
degrees  above  the  highest  temperature  noted  before  injec- 
tion. 

It  is  often  a  question  of  judgment  as  to  whether  a  re- 
action is  positive  or  not,  especially  in  those  cases  in  which 
the  increase  just  reaches  the  standards  assumed.  In  those 
cases,  all  circumstantial  features,  including  especially  the 
character  of  the  temperature  curve,  must  be  taken  into  con- 
sideration. In  no  case  should  the  decision  of  such  doubtful 
cases  be  left  in  the  hands  of  persons  who  are  not  thoroughly 
familiar  with  such  work.  The  limitations  of  the  test  must 
be  recognized,  and  the  results  must  always  be  interpreted 
with  judgment. 

In  making  the  test,  conditions  should  be  kept  as  nearly 
normal  as  possible.  The  herd  should  be  kept  quiet,  fed,  and 
watered  as  usual,  unless  the  manner  of  watering  would  per- 
mit them  to  drink  large  quantities  of  cold  water,  which 
might  vitiate  the  results  by  excessive  reduction  of  tempera- 
ture. Preferably  water  should  be  given  in  small  quanti- 
ties, if  it  is  cold. 

Animals  that  show  a  doubtful  reaction  should  be  retested 


TUBERCULOSIS  ^  287 

after  sixty  daj's.  If  the  retest  is  made  at  an  earlier  time,  it 
is  likely  to  be  less  reliable,  owing  to  the  effect  of  the  first 
dose  of  tuberculin.  On  the  retest  a  triple  dose  of  tubercu- 
lin should  be  used,  and  the  temperatures  after  the  injection 
should  be  begun  by  the  fourth  hour,  since  the  reaction  is 
likely  to  appear  earlier  than  in  the  original  test. 

Animals  recently  infected  but  not  yet  containing  diseased 
tissues,  i.  e.,  those  in  the  incubation  stage  or  those  in  which 
the  disease  is  dormant,  do  not  as  a  rule  react  to  the  test, 
while  those  in  which  the  disease  is  far  advanced  often  .fail 
to  react  because  they  are  already  saturated  with  the  tuber- 
culin naturally  formed  as  a  result  of  disease. 

The  disease  in  the  latter  can  be  recognized  by  a  physical 
examination;  in  the  former  only  by  a  repetition  of  the  test 
at  intervals  so  as  to  determine  its  presence  before  it  has 
made  such  headway  as  to  make  the  animal  a  source  of 
danger. 

The  purely  mechanical  part  of  the  test  can  be  carried  out 
by  any  intelligent  farmer.  He  should  learn  how  to  read  the 
thermometer  accurately  and  acquaint  himself  with  all  the 
details  of  the  test.  No  farmer  need  neglect  the  testing  of 
his  herd  because  of  the  inability  to  obtain  a  veterinarian, 
or  on  account  of  expense.  The  advantage  of  being  able  to 
test  one's  own  herd  is  great,  since  retests  can  be  made  on 
single  animals  as  the  occasion  seems  to  warrant,  and  all 
animals  purchased  can  be  tested  before  they  are  placed 
with  the  herd. 

Freeing  the  herd  from  tuberculosis. — The  methods  to  be 
followed  depend  on  the  value  of  the  animals,  and  the  extent 
of  the  disease  in  the  herd.  If  but  few  animals  are  found 
to  be  infected,  the  cheapest  and  most  effective  way  is  to 
remove  them.  If  a  larger  portion  is  diseased,  and  espe- 
cially when  the  animals  are  valuable  for  breeding  purposes, 
the  herd  may  be  separated  into  healthy  and  reacting  sec- 


288  .AGRICULTURAL  BACTERIOLOGY 

tions,  which  should  be  kept  in  separate  quarters  and  pas- 
tures. The  calves  from  tubercular  animals  should  be  re- 
moved at  birth,  placed  with  the  healthy  portion  of  the  herd, 
and  fed  on  the  milk  of  healthy  animals,  or  on  that  of  the 
tubercular  animals  after  proper  sterilization.  In  almost  all 
cases,  calves  so  treated  can  be  raised  to  maturity  in  a 
healthy  condition.  As  the  herd  is  built  up  in  this  way,  the 
old  reacting  animals  can  be  discarded ;  by  this  means  the 
valuable  characteristics  of  the  particular  family  can  be 
transmitted  through  the  progeny.  This  method  of  "weed- 
ing out"  the  disease,  instead  of  "stamping"  it  out  by  whole- 
sale slaughter,  is  known  as  the  Bang  system,  and  has  been 
widely  used  in  Denmark,  where  the  percentage  of  affected 
animals  is  so  high  that  immediate  slaughter  would  be  almost 
prohibitive. 

If  50  per  cent,  or  more  of  the  animals  react  to  the  test, 
it  is  advisable  to  consider  the  entire  herd  as  infected,  and 
not  attempt  to  eradicate  by  separation  and  slaughter,  but 
to  build  up  the  healthy  herd  by  the  progeny  alone.  This 
plan  is  recommended  because  it  has  been  found  by  experi- 
ence that  when  so  large  a  part  of  the  herd  reacts  to  the  test, 
most  of  the  remaining  animals  will  react  later. 

Many  of  the  States  recpiire  the  removal  of  known  tuber- 
cular animals  from  dairy  herds.  In  most  cases  the  State 
bears  a  part  of  the  loss  by  compensating  the  owner  in  part 
for  diseased  or  reacting  animals.  The  reacting  cattle  are 
usually  slaughtered  at  some  abattoir  in  which  federal  in- 
spectors are  stationed.  The  meat  of  reacting  animals  may 
or  may  not  be  passed  as  fit  for  food,  depending  upon  the 
extent  of  the  lesions  of  the  disease.  It  was  formerly  the 
custom  to  destroy  all  carcasses  of  reacting  animals,  but  this 
economic  loss  is  no  longer  sanctioned.  In  the  incipient 
stages  of  the  disease  the  atfected  parts  are  usually  confined 
to  definite  organs,  and  if  those  are  removed,  no  danger 


TUBERCULOSIS  289 

exists  in  the  use  of  meat  that  has  passed  federal  inspection. 
This  salvapre  lias  reduced  to  a  marked  extent  the  cost  of  the 
eradication  of  tuberculosis. 

The  basis  for  the  compensation  of  stockmen  by  the  State 
is  the  sanitary  importance  of  the  disease,  and  the  necessity 
of  safcfruardin*!:  Ilie  public  welfare  as  well  as  tlie  economic 
relations.  In  determininir  this  amount,  the  proportion  paid 
l)y  the  State  should  not  be  too  larjre  or  otherwise  there  is 
danger  that  the  pul)lic  treasury  will  be  made  the  victim 
of  unscrupulous  design. 

Farmers  do  not  appreciate  the  losses  that  are  occasioned 
])y  this  disease,  as  its  course  is  slow  and  insidious.  If  it 
ran  as  rapid  a  course  as  the  more  acute  communicable  dis- 
eases, its  importance  woidd  l)e  more  appreciated.  With  the 
develoj)ment  of  an  unthrifty  condition,  the  farmer  is  apt 
to  disi)ose  of  the  animal  to  someone  else,  which  simply  per- 
petuates the  disea.se  in  another  herd.  Many  are  sold  as 
"canners."  If  the  time  ever  comes  when  the  losses  due  to 
the  condemnation  of  carcasses  because  of  tuberculosis  is 
placed  on  the  producer  instead  of  on  the  consumer  of  meat, 
farmers  will  be  forced  to  the  necessity  of  eradicating  this 
plague  to  save  themselves  from  such  economic  losses  as  now 
obtain.  The  rapid  spread  of  the  disease,  especially  in  hogs, 
makes  this  problem  already  a  factor  of  considerable  im- 
portance in  the  price  paid  for  swine. 

Vaccination. — ]\Iany  attempts  have  been  made  to  use  vac- 
cines iji  the  prevention  of  tuberculosis,  but  without  success. 
Some  of  the  methods  emploj^ed  have  imparted  a  certain  de- 
gree of  immunity;  but,  because  of  the  fact  that  the  pro- 
tection persisted  for  only  a  few  months,  and  it  could  be  be- 
stowed only  on  young  animals,  the  methods  have  not  been 
a  practical  success. 

Prevention. — There  is  no  doubt  that  a  breeding  herd  free 
from  tuberculosis  is  a  most  valuable  asset,  and  one  that  will 


290  AGRICULTURAL  BACTERIOLOGY 

increase  in  value  as  people  become  more  alive  to  the  eco- 
nomic importance  of  the  disease,  and  seek  to  purchase  only 
sound  cattle.  At  present  it  is  difficult,  if  not  impossible,  to 
avoid  the  introduction  of  tuberculosis  into  a  herd  where 
considerable  numbers  of  cattle  are  purchased.  The  wide- 
spread distribution  of  the  disease,  even  though  sparingly 
present  in  any  particular  herd,  always  raises  the  question 
as  to  whether  any  animal  purchased  from  such  a  herd  may 
not  be  in  the  incipient  but  non-reacting  stage.  The  limita- 
tions of  the  tuberculin  test  are  such  that  it  will  not  enable 
one  to  recognize  every  case,  no  matter  in  what  stage  the 
disease  may  be.  Individual  animals  may  show  a  plainly 
negative  reaction  to  the  test  at  the  time  of  purchase  be- 
cause of  the  dormant  form  of  the  disease,  because  the  period 
of  incubation  has  not  been  completed,  or  because  of  dis- 
honest practices  by  the  seller.  These  animals,  if  main- 
tained in  the  herd,  are  quite  certain  in  time  to  develop  open 
tuberculosis,  and  be  a  source  of  loss  if  their  condition  is  not 
detected. 

The  only  effective  way  to  prevent  the  introduction  of  the 
disease  is  to  purchase  only  from  herds  that  are  known  to  be 
absolutely  free  from  tuberculosis.  It  is  certain  that  loss 
can  be  largely  avoided  by  the  testing  of  all  animals  at  the 
time  of  purchase,  by  keeping  the  animals  separate  from  the 
herd  for  at  least  three  months  with  a  retest  at  the  end  of 
this  period,  and  by  the  annual  testing  of  the  entire  herd. 
In  this  way,  the  use  of  tuberculin  serves  as  a  cheap  kind  of 
stock  insurance,  and  should  be  maintained  regularly  as  an 
annual  duty  in  the  herd.  Where  such  vigilance  is  prac- 
tised, little  danger  from  the  disease  need  be  feared. 

Tuberculosis  of  hogs. — As  has  been  stated,  the  infection 
of  the  hog  takes  place  with  the  greatest  ease  by  way  of  the 
alimentary  tract,  hence  the  lesions  are  most  likely  to  be 
found  in  the  glands  of  the  throat,  or  in  the  mesenteric 


TUBERCULOSIS  291 

glands.  The  bacilli  are  almost  entirely  of  bovine  origin, 
the  hog  coming  in  contact  with  them  in  the  manure,  or  in 
skim  milk  and  whey.  Due  to  the  fact  that  hogs  are  not 
kept  for  long  periods  of  time,  there  is  little  opportunity  for 
the  disease  to  make  such  progress  as  to  permit  the  animal 
to  eliminate  the  bacilli;  hence  there  is  probably  little,  if 
any,  direct  infection  from  one  hog  to  another. 

The  disease  can  be  detected  in  the  living  animal  most 
easily  by  the  intradermal  tuberculin  test,  which  avoids  the 
factor  that  makes  the  thermal  tuberculin  test  unsatisfactory 
— namely,  the  rapid  and  wide  variation  in  temperature  of 
the  hog. 

Avian  tuberculosis. — It  is  certain  that  tuberculosis  has 
made  rapid  progress  in  barnyard  fowl  in  this  country  in 


Fig.  51.     Avian  Tuberculosis 

A  section  throush  the  breast  of  a  healthy  bird  and  a  section  througli  that  of  a 

bird  that  died    from   tiibercuU)sis.      On    account    of  the   extreme  emaciation   the 

disease   is    frequently    called    "  going   light " 

recent  years,  due  undoubtedly  to  the  commerce  in  breeding 
birds.  In  many  sections  of  the  country  it  is  becoming  of 
great  economic  importance,  in  some  instances  causing  the 
death  of  50  per  cent,  of  the  flock  in  a  year. 

The  disease  is  characterized  by  the  extreme  emaciation 
of  the  bird  in  the  last  stages,  and  by  paleness  of  the  comb 
and  wattles.  Lameness  is  also  an  indication,  since  the 
joints  are  often  affected.     These  manifestations  of  the  dis- 


292 


AGRICULTURAL  BACTERIOLOGY 


ease  have  given  rise  to  the  terms  going  light  and  rheuma- 
tism. Unlike  mammalian  tuberculosis,  post-mortem  changes 
of  the  disease  are  found  chiefly  in  the  abdominal  cavity. 
The  liver  is  often  dotted  with  yellow  necrotic  areas,  which 
has  caused  the  expression  spotted  liver  to  be  commonly  used. 


Fig.  52.     Avian  Tuberculosis 

A   tubercular   liver.     The   organ    is   greatly    enlarged.     The   yellow    areas    give 

rise  to  one  of  the  common  names  applied  to  the  disease,   spotted  liver 

This  organ  is  often  much  increased  in  size.  The  spleen  is 
usually  enlarged  and  frequently  abnormal  in  shape.  On 
section,  the  normal  tissue  may  be  found  to  be  almost  wholly 
destroyed.  The  intestinal  wall  may  be  studded  with  tuber- 
cles of  varying  size.  In  the  more  advanced  cases  the  lesions 
will  be  found  in  other  organs,  such  as  the  kidneys,  lungs, 
and  ovaries. 


TUBERCULOSIS  293 

The  bacilli  are  eliminated  in  the  excreta,  and  infection  is 
by  way  of  the  alimentary  tract.  The  disease  is  spread  from 
flock  to  flock  by  the  sale  of  tubercular  birds,  and  possibly 
by  the  sale  of  eggs,  which,  when  the  ovaries  are  tubercular, 
may  contain  the  organisms.  The  chicks  hatched  from  the 
eggs  may  develop  the  disease,  a  case  of  hereditary  trans- 
mission. 

Tuberculosis  can  be  detected  with  some  degree  of  cer- 
tainty by  injecting  a  small  amount  of  tuberculin  prepared 
by  the  use  of  the  avian  tubercle  bacillus.  It  is  preferable 
to  avoid  the  purchase  of  stock  from  suspected  flocks,  and  to 
get  rid  of  the  entire  flock  when  the  disease  has  made  its  ap- 
pearance, rather  than  to  attempt  to  eradicate  it  in  other 
ways. 

There  is  no  reason  to  believe  the  disease  is  of  sanitary 
importance.  It  may  have  other  economic  aspects  than  those 
mentioned,  for  it  has  been  shown  that  the  ori/anism  is 
capable  of  producing  a  non-progressive  form  of  the  disease 
in  hogs  which  may  cause  the  rejection  of  certain  parts  by 
the  meat  inspectors.  To  avoid  such  trouble  and  to  prevent 
the  spread  of  the  disease  in  the  flock,  all  dead  birds  should 
be  buried,  so  that  thoy  can  not  be  eaten  by  hogs  or  birds. 

Differential  diagnosis. — There  are  a  number  of  diseases 
that  may  be  mistaken  for  tuberculosis  in  domestic  animals. 
Actinomj'cosis  may  produce  nodules  in  the  udder  that  re- 
semble tubercular  nodules.  Sheep  are  sometimes  affected 
by  an  intestinal  disease  known  as  nodular  disease,  which  to 
the  uninitiated  might  be  thought  to  be  tuberculosis,  but  is 
really  caused  by  a  parasitic  worm  which  burrows  into  the 
wall  of  the  intestine,  forming  a  greenish-colored  nodule 
about  the  size  of  a  pea. 

Johne's  disease. — As  has  been  mentioned,  there  are  a 
number  of  acid-fast  bacilli  other  than  the  tubercle  bacillus. 
The  disease,  known  as  Johne's  disease,  is  becoming  of  con- 


294  AGRICULTURAL  BACTERIOLOGY 

siderable  economic  importance  in  cattle.  It  is  a  very  slowly 
progressing  disease,  and  until  recently  no  method  of  de- 
tecting it  was  available  other  than  by  the  symptoms^  the 
most  marked  of  which  are  intermittent  diarrhea  and  pro- 
gressive emaciation.  The  symptoms  become  apparent  only 
after  the  disease  has  made  such  progress  that  the  organisms 
are  being  eliminated  from  the  affected  animal. 

The  isolation  and  cultivation  of  the  causal  organism  in 
pure  culture  has  made  it  possible  to  prepare  a  product  com- 
parable to  tuberculin  in  its  manner  of  preparation  and  use. 
This  diagnostic  agent  is  injected  into  the  blood  stream,  and 
causes  a  thermal  reaction  in  the  case  of  infected  animals. 
Its  use  has  been  limited.  It  can  not  be  said  at  this  time 
whether  it  will  be  possible  to  free  a  herd  from  the  disease 
through  the  detection  of  the  infection  in  the  individual  ani- 
mal before  the  organisms  are  eliminated. 


CHAPTER  XXII 

TEXAS  FEVER,  CONTAGIOUS  ABORTION,  AND 
FOOT-AND-.AIOLTIl  DISEASE 

Communicable  diseases  of  both  man  and  the  lower  ani- 
mals are  caused  not  only  by  microorganisms  usually  classed 
as  plants,  but  by  microscopic  animals,  the  protozoa.  Ma- 
laria and  sleeping-sickness  are  among  the  important  human 
diseases  caused  by  protozoa,  and  Texas  fever  is  the  most 
important  protozoal  animal  disease. 

The  pathogenic  protozoa  may  be  found  in  the  intestines, 
and  are  then  eliminated  in  the  feces,  from  which  there  is 
opportunity  for  them  to  find,  their  way  into  the  bodies  of 
healthy  animals.  Another  class  of  protozoa  are  to  be  found 
in  the  blood,  and  are  transmitted  from  one  animal  to  an- 
other by  biting  insects.  The  anopheles  mosquito  is  re- 
sponsible for  the  transmission  of  the  malarial  organism,  and 
one  of  the  cattle  ticks  for  the  transmission  of  the  Texas 
fever  organism.  In  the  case  of  diseases  transmitted  by  in- 
sects, there  is  opportunity  for  widespread  distribution, 
while  in  the  case  of  the  diseases  caused  by  intestinal  forms, 
the  chance  of  the  organism  gaining  entrance  to  the  tissues  of 
a  susceptible  host  is  much  smaller.  The  fight  against  the 
spread  of  the  insect-borne  protozoal  diseases  is  a  fight 
against  the  transmitting  insect,  the  tick  in  the  case  of  Texas 
fever. 

Texas  fever.— The  parasite  is  found  in  the  red  blood- 
cells,  which  are  destroyed  by  it,  and  the  red  coloring  mat- 
ter, the  hemoglobin,  is  set  free  to  be  eliminated  from  the 
body  in  the  urine,  to  which  it  imparts  a  red  or  black  color. 

295 


296  AGRICULTURAL  BACTERIOLOGY 

The  disease  is  often  called  tick  fever  because  of  the  method 
of  transmission,  and  red  or  black  water  from  the  dark  urine. 
Of  the  ticks  that  are  to  be  found  on  cattle,  but  one,  Mar- 
garopus  annidatus,  is  concerned  in  the  transmission.  The 
female  tick  that  is  infected  with  the  parasitic  organism 
drops  off  the  host  animal  to  lay  the  eggs  on  the  ground, 
where  they  hatch  in  from  thirteen  days  to  six  weeks,  de- 
pending on  the  temperature.  If  the  young  seed  ticks  come 
in  contact  with  an  animal,  they  attach  themselves  to  the 
inside  of  the  thighs  and  flanks,  along  the  belly  and  brisket, 
inside  the  fore  legs,  and  around  the  base  of  the  tail.  They 
remain  attached  to  the  animal  with  which  they  come  in  con- 
tact, living  on  the  blood. 

The  protozoa  causing  the  disease  pass  from  the  female 
into  the  egg,  and  thence  into  the  seed  tick,  which  infects  the 
host  animal.  If  the  host  is  immune,  no  harm  results;  but 
if  the  animal  is  susceptible,  a  fatal  form  of  the  disease  is 
usually  produced.  Young  animals  are  not  very  susceptible 
to  the  disease.  When  raised  in  contact  with  the  ticks,  they 
gradually  become  infected  with  the  protozoa  during  the 
time  when  the  immunity  is  so  high  that  a  fatal  form  of  the 
disease  is  not  occasioned,  and  a  permanent  immunity  is 
produced  by  the  mild  attack.  The  loss  from  the  disease  is 
not  so  much  from  death  of  animals  as  from  the  fact  that 
cattle  can  not  be  sent  from  infected  regions  to  free  areas. 
Thus  Southern  cattle  can  not  be  shipped  to  the  Northern 
cattle  markets,  except  under  certain  restrictions  that  add  to 
the  cost  of  marketing.  In  the  markets  the  cattle  from  in- 
fected regions  are  sold  at  a  lower  price  than  the  same  grade 
from  a  non-infected  territory.  The  ticks  are  also  a  con- 
stant drain  on  the  vitality  of  the  animals,  diminishing  the 
milk  production  and  rate  of  growth.  The  susceptibility  of 
cattle  from  free  territory  is  so  great  that  they  can  not  be 
taken  into  infected  territory  without  immunization.     This 


TEXAS  FEVER  297 

fact  has  limited  the  improvement  of  the  Southern  cattle  by 
the  introduction  of  pure  bred  animals  from  the  North. 

Eradication. — It  is,  of  course,  impossible  to  allow  the  free 
shipment  of  tick-infested  cattle  into  the  Northern  States, 
where  they  w^ould  be  brought  in  contact  with  susceptible 
animals.  Before  the  nature  of  the  disease  was  recognized, 
such  shipments  made  in  the  summer  caused  great  losses  in 
Illinois  and  Indiana.  In  1891  the  Texas-fever  line  was 
established,  marking  the  boundary  between  the  sections  free 
from  the  transmitting  tick  and  those  in  which  it  is  still 
present.  The  line  is  not  a  fixed  one,  but  changes  from  year 
to  3'ear  as  the  work  in  tick  eradication  progresses.  The 
methods  formerly  used  to  free  the  cattle  from  ticks  were 
l)ased  on  the  life  history  of  the  insect.  The  female  deposits 
her  eggs  on  the  ground.  The  shortest  period  reciuired  for 
the  eggs  to  hatch  is  twenty  da^'s.  The  young  ticks  that  do 
not  succeed  in  attaching  themselves  to  an  animal  die  from 
starvation.  The  period  required  to  insure  the  destruction 
of  the  ticks  by  starvation  is  dependent  on  moisture  and 
temperature  conditions.  In  general,  moisture  and  cold 
prolong  while  dryness  and  heat  shorten  the  period  the  ticks 
will  live  on  a  pasture.  This  period  is  important,  since  one 
of  the  wa^'s  of  freeing  cattle  from  ticks  is  to  place  them  on 
one  pasture  for  a  short  period,  then  on  another,  and  not 
return  them  to  the  first  until  starvation  has  destroyed  the 
ticks. 

By  a  proper  rotation  on  tick-free  pastures  the  cattle  can 
be  freed  from  ticks.  The  cattle  must  not  be  allowed  to  re- 
main on  one  pasture  longer  than  twenty  days,  since  this  is 
tlie  shortest  time  in  which  the  young  ticks  appear  after  the 
females  have  dropped  from  the  cattle  to  lay  the  eggs.  This 
method  is  a  long  and  somewhat  uncertain  one  to  employ 
when  large  areas  are  to  be  made  free  from  the  tick.  It  has 
been  largely  supplanted  by  dipping  the  animals  in  a  solu- 


298 


AGRICULTURAL  BACTERIOLOGY 


tion  of  sodium  arsenite,  which  destroys  the  tick  without 
injuring  the  animal.  The  animals  are  dipped  every  two 
weeks  from  March  to  November.  If  the  work  is  carefully 
and  systematically  done,  the  area  in  which  all  animals  have 
been  dipped  will  be  free  from  the  tick  and  will  no  longer  be 


h 

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Fig.  53.     Texas  Fever 

The   heavy  black   line   bounds   the   area    in   which   the   disease-transmitting   tick 

was  present  in  1906.     The  white  areas  below  this  line  have  been  freed  from  the 

tick  and  the  disease  between  1906  and  1918 

under  the  burdensome  regulations  that  so  hamper  the  tick- 
infested  areas. 

The  total  area  rendered  free  from  the  tick  since  the  be- 
ginning of  the  work  in  1906  to  December,  1918,  embraced 
458,529  square  miles.  It  seems  reasonably  certain  that 
within  a  few  years  Texas  fever  will  be  eradicated  from  this 
country.  The  work  of  eradication  should  progress  rapidly 
when  the  stockmen  realize  the  great  economic  advantages 
that  will  accrue  to  the  industry  from  the  eradication. 
Texas  fever  is  a  disease  the  eradication  of  which  simply 
awaits  the  practical  application  of  knowledge  already  ac- 
quired ;  while,  in  the  case  of  other  important  communicable 


TEXAS  FEVER  299 

diseases,  the  information  is  not  yet  sufficiently  complete,  so 
that  effective  measures  can  be  carried  out,  or  else  the  nature 
of  the  diseases  is  such  that  there  seems  little  hope  of  getting 
rid  of  them  in  the  near  future. 

Immunization. — The  youn^r  animal  is  not  very  susceptible 
to  Texas  fever,  and  can  be  readily  immunized  by  introduc- 
ing into  the  blood  a  small  number  of  the  causal  organisms 
that  will  not  produce  a  fatal  form  of  the  disease,  but  will 
cause  a  sufficient  degree  of  immunity  to  protect  against 
natural  infection.  The  requisite  number  of  organisms  may 
be  introduced  by  transferring  blood  from  an  infected  ani- 
mal to  the  animal  to  be  immunized.  The  amount  of  the 
blood  to  be  thus  transferred  depends  on  the  susceptibility 
of  the  animal.  If  an  old  animal  is  to  be  immunized,  one 
cubic  centimeter  of  the  blood  is  used,  but  if  a  yearling  is 
to  be  treated,  three  cubic  centimeters  of  the  blood  may  be 
employed  without  danger. 

Again,  the  tick  itself  may  be  allowed  to  infect  the  ani- 
mal, the  number  of  organisms  introduced  being  governed 
by  the  number  of  ticks  placed  on  the  animal.  The  method 
of  immunization  with  blood  is  very  successful,  about  3  per 
cent,  being  lost  by  vaccination  and  7  per  cent,  by  subse- 
quent infection.  The  10  per  cent,  loss,  when  compared  with 
the  90  per  cent,  loss  that  resulted  when  non-immunized 
cattle  were  placed  on  tick-infested  pastures,  is  a  measure  of 
the  success  of  the  treatment. 

Certain  cattle,  as  those  of  India,  are  resistant  to  the  dis- 
ease, and  attempts  have  been  made  to  breed  strains  that 
possess  such  an  immunity. 

Contagious  abortion. — The  term  abortion  signifies  the 
premature  discharge  of  the  fetus.  If  the  abortion  occurs 
late  in  the  gestation  period,  so  that  the  young  may  live,  it 
is  often  termed  premature  birth;  there  is,  however,  no  es- 


300  AGRICULTURAL  BACTERIOLOGY 

sential  difference,  as  far  as  the  cause  is  concerned,  between 
abortion  early  in  the  gestation  period  and  that  which  occurs 
later. 

Causes  of  abortion.— The  expulsion  of  the  fetus  may  be 
due  to  slipping,  injury  by  another  animal,  or  other  me- 
chanical causes,  and  to  feeds  that  have  a  specific  action  on 
the  pregnant  animal,  such  as  grains  and  fodders  that  con- 
tain large  amounts  of  smut  or  ergot.  It  is  quite  certain, 
however,  that  abortion  as  it  is  observed  in  cattle  is  almost 
wholly  due  to  the  invasion  of  the  animal  by  a  specific  or- 
ganism which  may  pass  from  animal  to  animal,  producing 
what  is  commonly  known  as  contagious  abortion.  The  dis- 
ease is  of  the  greatest  economic  importance  in  cattle.  A 
similar  trouble,  caused,  however,  by  a  different  organism, 
is  noted  in  mares,  and  a  third  organism  is  responsible  for 
abortion  in  sheep. 

The  disease  as  it  appears  in  cattle  has  spread  rapidly  in 
recent  years,  owing  to  the  great  increase  in  the  sale  of 
breeding  animals.  It  is  now  rare  to  find  a  herd  of  any 
considerable  size  that  has  an  entirely  clean  record.  The 
losses  it  occasions  are  felt  especially  bj^  the  breeder  who 
relies  on  the  progeny  of  his  herd  for  a  large  share  of  his 
returns,  much  more  than  by  the  farmer  who  is  primarily  in- 
terested in  the  production  of  milk.  In  the  beef  districts 
the  disease,  of  course,  becomes  of  major  importance  to  the 
farmer. 

The  loss  is  not  wholly  confined  to  that  incurred  from  the 
death  of  the  calf,  for  if  the  abortion  occurs  early  in  the 
gestation  period,  the  animal  will  rarely  prove  a  profitable 
producer  of  milk  during  that  lactation  period.  If  the  abor- 
tion occurs  late  in  the  period,  the  flow  of  milk  will  be  nor- 
mal. In  economic  importance  the  disease  ranks  with  tu- 
berculosis, Texas  fever,  and  hog  cholera.  Against  these 
the  farmer  has  much  hope  of  making  a  successful  fight  with 


ABORTION  301 

the  knowledge  that  is  already  available,  but  against  con- 
tagious abortion  the  case  is  far  less  hopeful. 

The  cause  of  bovine  abortion  is  a  small  bacillus  that  does 
not  form  spores  and  is  relatively  non-resistant  to  disin- 
fectants. It  is  called  B.  abortus,  or  the  Bang  organism, 
after  the  Danish  veterinarian  who  first  discovered  it.  The 
organism  has  been  found  widely  distributed  in  all  parts  of 
the  world,  and  there  is  no  doubt  concerning  its  causal  rela- 
tion to  the  bovine  form  of  the  disease. 

Nature  of  the  disease. — The  disease  is  one  that  has  a  spe- 
cific action  on  the  pregnant  animal,  causing  an  inflamma- 
tion of  the  uterus,  with  injury  to  the  fetus  or  causing  its 
death.  The  general  health  of  the  animal  is  not  affected  to 
any  noticeable  extent.  The  organism  is  eliminated  at  the 
time  of  abortion,  and  for  an  indefinite  period  thereafter  in 
the  discharges  from  the  uterus.  It  has  also  been  found 
in  the  milk. 

The  organism  may  be  present  for  months  before  abortion 
actually  occurs,  indicating  that  it  is  to  be  looked  upon  as  a 
chronic  disease.  Again,  an  animal  may  continue  to  elimi- 
nate the  abortion  bacilli  in  the  milk  years  after  the  last 
abortion  occurred  or  wh'en  no  abortion  has  been  known  to 
occur.  The  infection  of  an  animal  does  not  necessarily  pro- 
duce abortion,  since  this  will  depend  on  the  extent  of  in- 
jury to  the  fetus.  The  infected  animals  that  do  not  abort 
may  be  as  dangerous  to  healthy  animals  as  those  that  have 
aborted.  The  fact  that  some  unsuspected  animals  may  thus 
act  as  bacillus  carriers  makes  it  an  especially  difficult  dis- 
ease to  control  in  a  herd. 

The  natural  manner  of  infection  is  not  known  with  cer- 
tainty. It  has  been  shown  by  experimental  methods  that 
the  infection  may  occur  through  the  genital  passages.  It 
is  probable  that,  if  infection  occurs  in  this  manner,  it  must 
take  place  before  or  very  shortly  after  conception,  as,  after 


302  AGRICULTURAL  BACTERIOLOGY 

the  uterus  is  closed,  no  invasion  can  occur  through  the 
blood.  It  is  believed  by  many  that  the  male  is  one  of  the 
common  agencies  in  the  transmission  of  the  organism  from 
the  infected  to  the  healthy  animal.  It  has  also  been  shown 
that  infection  may  occur  through  the  alimentary  tract  by 
the  ingestion  of  contaminated  food.  By  some  it  is  thought 
that  this  is  the  most  important  if  not  the  sole  way  by  which 
the  organism  enters  the  body  under  natural  conditions. 
Infection  in  this  manner  may  occur  after  conception.  It 
will  be  evident  that  if  the  disease  is  introduced  into  a  herd, 
there  will  always  be  ample  opportunity  for  it  to  spread, 
whatever  the  method  by  which  the  organism  invades  the 
individual  animal,  since  the  stable  and  fodder  is  certain  to 
be  contaminated  with  the  organism. 

The  disease  may  be  introduced  into  the  herd  by  the  pur- 
chase of  an  infected  animal,  and  probably  by  the  feeding 
of  mixed  creamery  and  cheese  factory  by-products.  While 
this  last  method  of  spread  has  not  been  proved,  the  pres- 
ence of  the  organism  in  the  milk  of  a  considerable  propor- 
tion of  the  infected  animals,  and  the  fact  that  infection 
can  occur  by  way  of  the  alimentary  tract,  would  lead  to 
the  conclusion  that  this  may  be  one  method  by  which  the 
disease  is  being  distributed  from  farm  to  farm.  This 
method  of  distribution  can  easily  be  avoided  by  pasteuriz- 
ing the  factory  by-products,  a  method  equally  effective 
against  both  tuberculosis  and  foot-and-mouth  disease. 

Detection  of  the  diseased  animal. — Among  the  anti- 
bodies formed  by  the  cells  of  an  infected  animal  are  sub- 
stances to  which  the  term  agglutinin  has  been  applied. 
These  substances  possess  the  property  of  causing  the  bac- 
teria producing  the  disease  to  clump  or  to  come  together  in 
large  aggregates.  The  clumping  of  the  cells  may  be  deter- 
mined by  examining  the  solution  under  the  microscope  or  by 
the  unaided  eye. 


ABORTION  303 

The  actual  tests  are  made  by  preparing  a  uniform  sus- 
pension of  the  cells  of  the  causal  organism  in  a  salt  solu- 
tion. A  small  quantity  of  blood  is  drawn  from  each  ani- 
mal to  be  tested,  the  blood  is  allowed  to  clot,  and  the  serum 
removed,  which  is  then  added  in  var^-ing  proportions  to  the 
suspension  of  bacterial  cells.  If  the  blood  is  free  from  the 
specific  agglutinin  produced  by  the  animal  on  invasion  by 
ihe  organism  of  abortion,  the  cells  remain  in  suspension.  If 
the  specific  agglutinin  is  present,  the  cells  clump  and  the 
masses  soon  settle,  leaving  a  clear  liquid.  The  agglutinin 
can  be  developed  only  as  the  host  has  been  invaded  by  the 
organism.  A  positive  test  does  not  imply  that  the  animal  at 
the  moment  the  blood  was  drawn  was  harboring  the  organ- 
ism, for  the  anti-bodies  persist  Ion*:  after  the  organism  has 
disappeared  from  the  body.  Similar  tests  are  used  in  the 
detection  of  typhoid  fever  in  man,  glanders  in  horses,  and 
white  diarrhea  in  chickens. 

A  test  for  another  of  the  anti-bodies  is  also  used  in  the 
detection  of  animals  that  are  or  have  been  affected  with 
B.  abortus.  The  test  is  so  complicated  that  it  can  not  be 
described  here.  It  is  similar  to  the  Wassermann  test  used 
for  the  detection  of  syphilis  in  humans.  It  is  also  known 
as  the  complement  fixation  test.  It  involves  the  use  of  the 
blood  corpuscles  or  serum  from  three  different  species  of 
animals  other  than  the  bovine  animal  that  is  being  tested. 
The  organism  causing  the  disease  is  also  used.  It  is  an 
example  of  the  progress  that  has  been  made  in  the  detection 
of  the  most  minute  quantities  of  specific  substances  of  un- 
known nature  formed  by  the  bod}'  cells  of  an  animal  in- 
vaded by  a  parasitic  organism. 

The  stock-owner  must  rely  for  protection  very  largely 
on  the  information  he  can  secure  as  to  the  health  of  the 
herd  from  which  he  intends  to  purchase. 

Control  and  prevention. — It  is  not  usual  for  an  animal 


304  AGRICULTURAL  BACTERIOLOGY 

to#abort  more  than  once  or  twice,  and  such  condition  is  fre- 
quently interpreted  as  an  indication  that  a  certain  degree 
of  immunity  has  developed  as  a  result  of  the  earlier  attack. 
It  seems  probable  that  this  is  not  the  case,  but  that  there  is 
an  age  immunity,  since  the  greatest  number  of  abortions 
occur  with  heifers  during  the  first  and  second  pregnancies. 
It  is  not  good  practice  to  sell  aborting  animals  with  the 
hope  of  getting  rid  of  the  disease,  since  it  will  rarely  if 
ever  succeed.  The  replenishing  of  the  herd  by  purchase 
will  serve  to  continue  the  trouble,  either  by  the  addition 
of  healthy  animals  to  become  infected,  or  by  the  introduc- 
tion of  new  centers  of  infection. 

IMany  treatments  have  L?en  devised  and  recommended 
for  the  prevention  and  cure  of  abortion.  For  example,  the 
internal  administration  of  carbolic  acid,  both  with  the  feed 
and  by  hypodermic  injection,  has  been  widely  used.  There 
is  little  reason  to  believe  that  it  has  any  favorable  effect. 
The  use  of  vaccines  has  been  attempted,  but  without  suc- 
cess. It  seems  evident  that  the  breeder  and  farmer  must 
rely  entirely  on  sanitary  precautions  to  prevent  the  spread 
of  the  disease.  He  must  seek  to  destroy  the  organism  in 
the  infectious  material  discharged  by  the  animal.  The  dead 
fetus  and  also  the  afterbirth  should  be  buried ;  the  contami- 
nated litter  should  be  destroj^ed ;  and  the  aborting  animals 
should  be  flushed  out  with  a  0.5  per  cent,  solution  of  some 
of  the  soapy,  coal-tar  disinfectants,  such  as  l^^sol,  or  with  a 
0.5  per  cent.  LugoUs  solution,  which  consists  of  one  part  of 
iodine  and  two  parts  of  potassium  iodide  dissolved  in  three 
hundred  parts  of  water.  The  solution  should  be  warmed 
to  100°  F.  The  treatment  should  be  continued  daily  until 
no  discharge  is  to  be  noted.  This  procedure  will  not  only 
serve  to  limit  the  distribution  of  the  organism,  but  will  be 
of  some  service  in  the  prevention  of  sterility,  which  is  a 
frequent  sequence  of  abortion,  and  an  important  factor  in 


FOOT  AND  MOUTH  DISEASE  305 

its  economic  importance.     It  is  also  well  to  disinfect  the 
bull  after  each  service. 

A  separate  maternity  stall  should  he  provided,  to  which 
all  animals  that  are  to  calve  at  the  normal  time  should  be 
removed.  This  stall  should  be  kept  clean,  and  supplied 
with  an  abundance  of  clean  bedding.  Animals  that  show 
signs  of  aborting  should  not  be  placed  in  this  stall,  but  re- 
moved from  the  stables  to  a  separate  building. 

Foot-and-mouth  disease. — There  are  a  number  of  trans- 
missible diseases  of  domestic  animals  prevalent  in  Europe 
that  are  not  found  in  this  country.  Among  them  are  con- 
tagious pleuro-pneumonia  of  cattle,  hog  erysipelas,  and  foot- 
and-mouth  disease,  which  affects  the  cloven-hoofed  animals 
and  man.  All  domestic  animals  imported  from  Europe 
must  be  kept  in  quarantine  for  a  considerable  period  in 
order  that  there  may  be  time  for  them  to  develop  symptoms 
of  any  disease  with  which  they  may  be  infected,  and  to 
permit  of  a  detailed  examination  as  to  their  health.  These 
precautions  are  taken  primarily  to  prevent  the  introduction 
of  diseases  that  are  not  known  in  this  country.  Even  with 
all  precaution,  there  is  always  opportunity  for  some  of 
these  diseases  to  be  introduced  and  to  spread  rapidly. 
Foot-and-mouth  disease  forms  a  striking  example.  There 
have  been  six  outbreaks  of  this  disease,  as  follows:  1870, 
1880,  1884,  1902-3,  1908-9,  1914-15.  The  disease  has,  how- 
ever, been  eradicated  at  each  appearance.  The  method  fol- 
lowed has  been  to  slaughter  not  only  the  diseased  animals, 
but  all  other  susceptible  animals  on  the  farms  on  which  the 
outbreaks  occurred.  In  1902-3  4,461  animals  were  killed; 
in  1908-9  3,636  animals  were  slaughtered.  The  cost  of  the 
eradication  of  each  of  the  outbreaks  in  1902-3  and  1908-9 
was  approximately  $300,000.  Not  a  large  amount  to  pay 
as  insurance  of  the  entire  stock  industry  of  this  country 
against  this  disease  for  ten  years. 


306  AGRICULTURAL  BACTERIOLOGY 

The  disease  is  like  other  acute  communicable  diseases  in 
that  it  has  an  ebb  and  flow.  These  waves  occur  at  intervals 
of  several  years.  The  reason  for  this  variation  in  severity 
is  not  known.  In  Germany,  after  a  period  in  which  the 
disease  was  not  especially  important,  it  began  its  ravages, 
and  in  1911,  3,000,000  cattle  were  affected,  1,000,000  sheep, 
and  2,500,000  hogs.  The  loss  from  death  of  animals  is  not 
great,  only  about  1  per  cent.  The  economic  losses  are  due 
to  the  loss  of  flesh,  to  diminished  milk  production,  or  to  loss 
of  reproductive  power.  It  has  been  estimated  that  for 
cattle  this  loss  ranges  from  seven  to  twenty  dollars  a  head, 
and  proportionately  less  for  smaller  animals.  It  is  thus 
clear  that  the  disease  imposes  a  great  economic  burden  upon 
stockmen,  and  if  by  the  expenditure  of  reasonable  sums 
the  country  can  be  protected  from  it,  it  is  certainly  wise 
to  spend  the  money. 

The  disease  presents  an  excellent  example  of  the  influence 
of  modern  commercial  conditions  on  the  rate  of  spread. 
The  infection  of  the  great  shipping-yards  is  an  especially 
important  factor  in  the  distribution.  The  outbreak  of  foot- 
and-mouth  disease  of  1908-09  was  due  to  the  importation 
from  Japan  of  vaccine  virus  that  was  used  in  one  of  the 
vaccine  establishments  in  Pennsylvania.  Some  of  the  virus 
was  sent  to  a  Detroit  establishment  that  rented  calves  from 
a  dealer  for  the  manufacture  of  smallpox  vaccine.  After 
the  animals  had  been  used  for  this  purpose  they  were  re- 
turned to  the  dealer  and  resold  by  him  to  farmers. 

Bovine  animals  inoculated  with  the  mixed  virus  of  cow- 
pox  and  foot-and-mouth  disease  develop  symptoms  of  cow- 
pox  alone,  but  when  brought  in  contact  with  healthy  ani- 
mals the  virus  of  foot-and-mouth  disease  may  spread  from 
the  animals  that  show  no  symptoms.  The  calves  in  ques- 
tion were  placed  in  pens  in  the  Detroit  stockyards,  and 
from  there  distributed  as  shown  in  the  diagram.     Four  days 


FOOT  AND  MOUTH  DISEASE  307 

later  a  shipment  of  cattle  was  placed  in  the  same  yards,  a 
portion  of  the  shipment  was  reshipped  to  Buffalo,  and  from 
there  a  number  of  animals  were  sent  to  two  towns  in  Penn- 
sylvania in  the  neighborhood  of  which  outbreaks  of  the 


Fijj.  .'54.     Foot-and-Mouth  Disease 
The  rapid  spread  of  disease  is  made  possible  by  modern  commercial  conditions 

disease  occurred  as  illustrated  in  the  diagram.  In  ten  days 
the  disease  had  traveled  hundreds  of  miles.  The  rapid 
and  effective  work  of  government  officials  saved  the  country 
at  that  time  from  the  permanent  introduction  of  the  disease. 
The  outbreak  of  1914-15  was  of  unknown  origin.  It  was 
first  noted  in  Michigan  on  October  15,  1914.  Within  ap- 
proximately one  month  it  had  invaded  nineteen  States  from 
Washington  in  the  AVest  to  Massachusetts  in  the  East. 
Some  weeks  later  three  additional' States  were  invaded  by 
the  disease.  This  unparalleled  rapidity  of  spread  was  due 
to  the  fact  that  the  great  stockyards  of  Chicago  became 
infected  early  in  the  outbreak.  The  stream  of  animals  into 
the  stockyards  is  continued  by  a  much  smaller  stream  of 
animals  leaving  the  yards  to  be  sent  to  all  parts  of  the 
country.  No  more  ideal  way  of  spreading  an  acute  disease 
could  be  devised,  and  no  more  marked  example  of  the  role 
of  modern  commerce  in  the  distribution  of  disease  has  ever 


308  AGRICULTURAL  BACTERIOLOGY 

been  offered  than  the  outbreak  of  the  foot-and-mouth  dis- 
ease in  1914-15. 

The  number  of  animals  slaughtered  was  152,157  in  3,021 
herds.  The  total  loss  occasioned  by  the  outbreak  amounted 
to  $5,619,346.     The  greater  part  of  this  sum  was  paid  to 


Fig,  55.     Foot-and-Mouth  Disease 

Sharply   delimited  eroded   areas   on   the  tongue   form  one   of  the  characteristic 

lesions  of  the  disease 

farmers  to  recompense  them  for  the  animals  slaughtered. 
This  amount,  large  as  it  may  seem,  is  not  much  to  pay  to 
insure  the  United  States  against  the  ravages  of  a  disease 
that  caused  an  estimated  loss  of  $5,000,000  to  the  stock  in- 
dustry of  England  in  one  year,  1883. 


FOOT  AND  MOUTH  DISEASE 


309 


Nature  of  the  disease. — The  causal  organism  is  an  ultra- 
microscopic  one.  In  from  three  to  six  days  after  the  animal 
is  exposed  to  the  infection,  the  disease  makes  its  appearance. 
The  onset  af  the  trouble  is  marked  by  chills,  followed  by 
fever  which  may  cause  the  temperature  to  rise  as  high  as 
106°  F.  In  one  or  two  days  blisters  or  vesicles  about  the 
size  of  a  hemp-seed  or  a  pea  are  to  be  noted  on  the  mucous 


¥\fr.  5fi.     Foot-and-Mouth  Disease 
Ulcers   between   the   toes    are   also    charattcristic   of   this   disease 

membranes  of  the  mouth,  tongue,  and  gums.  The  vesicles 
are  filled  with  a  yellowish,  watery  liquid  in  which  the  causal 
organism  is  present.  Similar  eruptions  appear  on  the  feet 
between  the  digits  and  above  the  coronet.  They  may  also 
appear  on  the  udder  and  teats.  The  milking  process  rup- 
tures the  vesicles,  and  the  organism  finds  its  way  into  the 
milk,  by  which  it  spreads  from  one  animal  to  another  and 
from  farm  to  farm  when  mixed  cheese  factory  or  creamery 
products  are  fed.     The  vesicles  increase  in  size  until  they 


310  AGRICULTURAL  BACTERIOLOGY 

reach  the  diameter  of  a  dime  or  even  larger.  They  rupture 
soon  after  their  appearance,  leaving  reddened  sensitive 
spots  or  erosions  behind.  Food  is  refused,  and  a  ropy  saliva 
drools  from  the  mouth.  The  soreness  of  the  feet  often  ren- 
ders it  impossible  for  the  animal  to  stand. 

The  disease  spreads  with  great  rapidity  in  the  herd.  The 
chance  that  all  of  the  herd  will  acquire  it  has  led  to  the 
inoculation  of  the  animals  by  the  transfer  of  some  of  the 
saliva  from  the  diseased  to  the  healthy  animals,  with  the 
idea  of  shortening  the  period  of  trouble  in  the  herd.  In 
cases  of  doubt  as  to  the  nature  of  the  disease,  the  inoculation 
of  a  calf  should  give  definite  information,  since  the  inocu- 
lation should  result  in  the  characteristic  vesicles  in  from 
twenty-four  to  seventy-two  hours. 

There  are  a  number  of  diseases  that  somewhat  resemble 
foot-and-mouth  disease.  Cowpox  forms  similar  vesicles,  but 
the  inoculation  does  not  result  in  symptoms  of  fever  and 
eruption  for  at  least  ten  days.  In  mycotic  stomatitis,  or 
inflammation  of  the  membranes  of  the  mouth,  the  entire 
mouth  cavity  is  inflamed  and  vesicles  are  rare;  if  present, 
they  do  not  increase  in  size.  The  thin  skin  between  the 
toes  may  be  inflamed,  but  the  vesicles  do  not  appear,  nor 
is  the  udder  affected.  The  disease  does  not  spread  and  the 
inoculation  of  calves  is  not  successful.  In  foot-rot  the  in- 
flammation of  the  foot  is  general,  and  the  mouth  remains 
unaffected.  In  ergotism,  or  trouble  due  to  the  eating  of 
too  great  quantities  of  smut,  the  mouth  is  not  affected,  and 
the  tissue  changes  are  to  be  noted  at  the  tips  of  the  ears, 
end  of  the  tail,  and  upon  the  lower  part  of  the  legs. 

Foot-and-mouth  disease  is  transmitted  to  man  by  the  use 
of  infected  milk.  It  causes  eruptions  in  the  mouth  and 
on  the  fingers,  but  is  seldom  fatal,  except  in  the  case  of 
weakened  children.     In  man  it  is  known  as  aphthous  fever. 


CHAPTER  XXIII 
RABIES  AND  ACTINOMYCOSIS 

Rabies. — As  has  been  shown,  the  losses  from  Texas  fever 
are  needless,  since  ways  are  known  by  which  it  can  be  com- 
pletely eradicated.  Rabies  is  a  disease  that  likewise  could 
be  made  to  disappear,  if  simple  procedures  that  could  easily 
be  carried  out  were  enforced. 

The  disease  is  primarily  one  of  the  flesh-eating  animals, 
but  is  transmissible  to  all  mammals  through  the  bite  of  a 
rabid  animal.  In  reality  it  is  transmitted  almost  wholly  by 
dogs,  since  the  dog  is  the  only  animal  that  is  allowed  to 
run  about  freely.  It  is  found  in  most  parts  of  the  world ; 
Australia  and  England  are  the  only  countries  that  are 
known  to  be  free  from  it,  and  they,  are  kept  so  through,  the 
rigid  enforcement  of  wise  quarantine  regulations  with  refer- 
ence to  the  importation  of  dogs.  In  the  United  States  it 
has  spread  rapidly  in  the  last  few  years,  until  at  present 
it  is  found  from  the  Atlantic  to  the  Pacific.  In  1908  it  is 
know:n  to  have  caused  the  death  of  111  people.  It  is  also 
of  considerable  economic  importance  because  of  the  loss  of 
domestic  animals.  The  sanitary  and  economic  aspects  of 
the  disease  are  small  when  compared  with  some  others,  but 
all  loss  is  so  unnecessary  that  it  seems  advisable  to  discuss 
the  disease  in  some  detail,  especially  since  there  are  so 
many  misconceptions  concerning  it. 

The  virus,  of  unknown  nature,  is  known  to  be  present  in 
the  saliva,  the  vitreous  humor  of  the  eye,  lymph,  milk,  urine, 
and  the  peripheral  nervous  sj^stem.  The  presence  of  the 
virus  in  the  saliva  is  the  explanation  of  the  transmission 

311 


312  AGRICULTURAL  BACTERIOLOGY 

by  the  bite  of  an  infected  animal.  Many  times  the  saliva 
is  so  completely  removed  from  the  teeth  of  the  rabid  animal 
that  none  of  the  organisms  is  introduced  into  the  wound. 
Especially  is  this  likely  to  be  true  when  the  wound  is  in- 
flicted through  the  clothing,  through  the  coat  of  a  long- 
haired dog,  or  through  the  wool  of  a  sheep.  This  is  one  of 
the  reasons  why  only  a  small  proportion  of  the  human  be- 
ings and  animals  that  are  bitten  by  rabid  animals  develop 
the  disease,  even  though  no  protective  treatment  is  em- 
ployed. 

The  virus  is  known  to  be  present  in  the  saliva  from  two 
to  five  days  before  the  symptoms  of  the  disease  are  evident. 
The  wounds  in  which  the  infection  is  most  likely  to  be  of  a 
serious  nature  are  those  inflicted  on  the  head  and  face  rather 
than  on  the  extremities.  The  virus  develops  in  the  nerves, 
and  is  more  likely  to  establish  itself  in  tissues  that  are  rich 
in  nerves  than  in  those  deficient  in  these  structures.  The 
extent  of  the  bites  is  also  an  important  factor  in  determin- 
ing whether  infection  is  to  occur,  since  the  amount  of  virus 
introduced  will  be  in  proportion  to  the  number  of  bites 
inflicted.  The  tissues  seem  to  have  the  power  of  destroy- 
ing a  limited  number  of  the  organisms.  Again,  if  the 
wounds  are  such  that  bleeding  is  marked,  there  will  be  a 
tendency  for  the  organisms  to  be  washed  out.  The  deep 
puncture  wounds  are  likely  to  be  more  serious  than  a  tear 
in  the  flesh. 

It  is  commonly  believed  that  there  is  a  seasonal  distribu- 
tion of  rabies,  that  it  is  more  common  during  the  so-called 
dog  days  of  late  summer.  There  is  little  or  no  basis  of  fact 
for  this  belief.  There  is,  however,  more  opportunity  for 
the  rabid  dog  to  come  in  contact  with  human  beings  and 
with  animals  in  the  summer  than  in  the  colder  months  when 
there  is  less  out-of-door  life.  The  regulations  that  require 
the  muzzling  of  dogs  for  a  few  weeks  in  the  summer  have 


RABIES  313 

no  justification  unless  the  period  is  extended  to  include  the 
entire  year. 

The  incubation  period  varies  considerably  in  length,  de- 
pending upon  the  location  and  extent  of  the  bites.  The 
symptoms  are  not  apparent  until  the  central  nervous  system 
is  involved.  The  rapidity  with  which  this  will  occur  is  de- 
pendent on  the  distance  of  the  bite  from  the  lirain.  The 
extent  of  the  bite  is  also  of  importance  in  determining  the 
rate  at  which  the  disease  progresses.  The  average  periods 
of  incubation  are  as  follows: 

Man     40  days 

Dog    21-4S  days 

Horsps     2«-.')6  days 

Cats  14-28  days 

Pigs    1 4-21  days 

Sheep     21-28  days 

The  virus  may  remain  dormant  after  its  introduction  into 
the  tissues  for  a  varying  period  of  time,  thus  delaying  the 
development  of  the  symptoms  for  months  and  possibly  years 
after  the  bite  is  inflicted. 

Symptoms. — Rabies  is  generally  divided  into  two  forms, 
furious  and  dumb.  In  the  first  the  animal  is  irritable  and 
bites  nearly  every  object  with  which  it  comes  in  contact; 
in  the  second  the  muscles  of  its  jaws  are  paralyzed  early 
in  the  attack,  and,  being  unable  to  bite,  the  animal  remains 
more  quiet.  The  two  forms  of  the  disease  represent  the  ex- 
tremes, and  all  gradations  are  to  be  noted  between  them. 
The  saliva  from  a  case  of  dumb  rabies  is  just  as  dangerous 
as  that  from  a  case  of  the  furious  type.  The  furious  type 
passes  into  the  dumb  type  as  the  disease  progresses,  owing 
to  the  paralysis  of  the  muscles. 

The  furious  type  is  marked  by  symptoms  of  nervousness. 
The  animal  may  be  more  restless  or  more  affectionate  than 
usual,  seeking  to  lick  the  hand  or  face.     If  an  abrasion  of 


314  AGRICULTURAL  BACTERIOLOGY 

the  skin  is  present  on  the  part  licked,  inoculation  with  the 
virus  may  result.  More  frequently  the  dog  seeks  to  be 
alone,  but  it  does  not  remain  quiet ;  it  often  acts  as  if  it 
were  being  annoyed  by  something,  snapping  and  howling  at 
some  imaginary  object.  The  animal  often  leaves  home^ 
and  on  its  journeyings  is  likely  to  infect  animals  and  human 
beings.  It  does  not  usually  go  out  of  its  way  to  bite. 
There  is  ample  opportunity  for  other  dogs  to  be  bitten  by 
it,  because  of  the  canine  custom  of  seeking  to  extend  ac- 
quaintances. 

Frothing  at  the  mouth  often  occurs,  and  the  voice  is  more 
of  a  howl  than  a  bark,  due  to  the  atfected  muscles  of  the 
throat.  The  rabid  animal  has  no  fear  of  water,  as  is  ex- 
pressed by  the  common  name  of  the  disease,  hydrophobia. 
Attempts  to  drink  cause  a  paroxysm  of  the  affected  mus- 
cles of  the  throat.  The  animal  can  not  swallow.  The  pa- 
ralysis of  the  muscles  gradually  extends  itself,  and  death 
finally  brings  relief.  Much  the  same  symptoms  are  noted 
in  man. 

In  the  dumb  type  the  nervous  symptoms  are  lacking  and 
the  paralysis  appears  very  early  in  the  course  of  the  disease. 
It  may  easily  be  mistaken  for  choking.  The  furious  form 
is  the  usual  type  noted  in  the  case  of  man  and  in  most  ani- 
mals other  than  the  rabbit,  which  is  used  extensively  in 
the  detection  and  prevention  of  the  disease. 

Diagnosis. — It  was  stated  that  only  about  10  per  cent, 
of  human  beings  bitten  by  known  rabid  animals  develop  the 
disease,  owing  to  the  non-introduction  of  the  organism  into 
the  tissues,  or  to  the  destruction  of  the  organisms  by  the 
tissues.  Death  from  rabies  presents  a  series  of  horrible 
symptoms,  and  if  a  person  is  severely  bitten,  the  preventive 
treatment  should  be  applied  without  delay.  It  is,  however, 
highly  advantageous  to  know  for  a  certainty  whether  the 
dog  that  has  inflicted  a  wound  is  actually  rabid  or  not. 


RABIES  315 

The  quickest  way  to  determine  with  certainty  the  nature 
of  the  trouble  is  to  confine  the  dog  and  note  the  symptoms. 
The  disease  is  invariably  fatal,  and  death  is  commonly  pre- 
ceded by  a  definite  sequence  of  symptoms,  so  that  there  can 
be  no  mistake  in  the  diagnosis.  The  diagnosis  should  be 
made  as  quickly  as  possible,  for  if  preventive  treatment  is 
to  be  applied,  it  must  be  administered  without  delay,  since 
it  is  of  no  avail  if  not  begun  until  the  symptoms  appear. 
If  it  is  impossible  to  secur,e  and  confine  the  dog  alive,  the 
diagnosis  can  be  made  by  a  microscopic  examination  of  the 
brain.  The  head  should  be  removed,  packed  in  ice  and 
sawdust,  and  sent  to  the  laboratory  that  is  maintained  by 
most  States  and  large  cities  for  such  work.  In  killing  the 
dog,  care  should  be  taken  not  to  injure  the  brain  or  spinal 
cord. 

Preventive  treatment. — The  treatment  used  to  prevent 
the  development  of  the  disease  in  persons  bitten  by  a  rabid 
animal  was  one  of  the  triumphs  of  Pasteur.  The  organism 
found  in  ordinary  cases  of  rabies  can  be  increased  in  viru- 
lence for  rabbits  by  passing  it  through  a  series  of  animals. 
The  so-called  fixed  virus  will  kill  a  rabbit  in  seven  days, 
when  introduced  beneath  the  membranes  of  the  brain.  If 
the  cord  is  removed  from  the  animal  immediately  after 
death  and  allowed  to  dry  over  caustic  potash,  the  virus  be- 
comes attenuated,  the  extent  of  the  attenuation  depending 
on  the  length  of  the  drying  process.  The  preventive  treat- 
ment consists  in  giving  hypodermic  injections  of  a' suspen- 
sion of  the  dried  cord.  The  first  injections  contain  mate- 
rial that  has  been  dried  for  about  two  weeks,  while  the  sub- 
sequent injections  are  made  with  material  that  has  been 
dried  for  a  shorter  period,  until  at  last  an  injection  of  the 
fresh  cord  can  be  given  without  danger.  Injections  are 
made  for  a  period  of  twenty-one  days.  Of  all  the  persons 
known  to  have  been  bitten  by  rabid  animals,  to  which  the 


316  AGRICULTURAL  BACTERIOLOGY 

preventive  treatment  has  been  administered  at  the  Pasteur 
Institute  in  Paris,  but  one-half  of  one  per  cent,  have  died 
of  rabies,  while  the  mortality  records  of  those  that  did  not 
receive  the  treatment  are  approximately  ten  per  cent. 

Wounds  inflicted  by  a  dog  known  to  be  rabid,  or  suspected 
of  the  disease,  should  be  cauterized  as  soon  as  possible  by  the 
application  of  concentrated  nitric  acid,  strong  carbolic  acid, 
or  by  a  hot  iron  when  the  chemical  agents  are  not  available. 
This  strenuous  treatment  will  destroy  the  tissue  about  the 
wound,  together  with  the  virus  that  has  been  introduced  by 
the  animal.  The  quicker  the  cauterization  is  carried  out, 
the  more  effective  it  will  be.  The  cauterization,  if  it  does 
not  completely  destroy  the  virus  in  the  tissue,  will  prolong 
the  period  of  incubation  and  thus  give  a  better  opportunity 
for  a  careful  diagnosis  to  be  made  and  for  the  preventive 
treatment  to  be  applied  in  time  to  be  successful. 

The  treatment  was  first  applied  to  a  human  being  by  Pas- 
teur in  1886.  Between  1886  and  1917,  48,107  people  were 
treated  at  the  Pasteur  Institute  in  Paris.  From  experience 
it  is  known  that  at  least  10  per  cent,  of  this  number  would 
have  died  from  rabies  if  the  protective  inoculation  had  not 
been  administered.  Actually  but  137  of  this  great  number 
died  from  rabies.  Pasteur  has  to  his  credit  the  saving  in 
his  own  laboratory  of  4,673  people  from  a  most  horrible 
death.  Similar  laboratories  were  soon  established  in  all 
parts  of  the  world.  The  total  number  of  people  saved  from 
rabies  reaches  many  thousands. 

Eradication. — Since  the  disease  is  transmitted  almost  en- 
tirely by  the  dog,  it  could  be  prevented  and  eradicated  by 
keeping  all  dogs  that  are  allowed  their  freedam  muzzled  at 
all  times.  The  effect  of  such  measures  is  shown  by  the 
history  of  rabies  in  England.  The  following  figures  repre- 
sent the  number  of  reports  of  the  disease : 


RABIES  317 

1805    672  cases 

1808    17  cases 

1901     1  cases 

1903-7    0  cases 

This  reduction  was  due  to  the  enforcement  of  muzzling 
laws  after  1896.  Rabies  was  reintroduced  into  Eno:land 
in  1919  by  aviators  who  were  able  to  disregard  the  quaran- 
tine regulations.  The  muzzling  regulations  that  have  been 
passed  by  governing  bodies  in  this  country  are  rarely,  if 
ever,  enforced  in  an  effective  manner,  because  many  people 
believe  it  cruel  to  muzzle  a  dog.  It  is  certain  that  the  dis- 
ease could  be  eradicated  in  a  short  time  if  its  transmission 
could  be  prevented.  It  is  also  certain  that  the  muzzling 
of  dogs  for  a  short  time  would  be  much  more  humane  than 
to  have  hundreds  of  them,  as  well  as  other  animals  and 
people,  dying  from  rabies  each  j'car. 

Actinomycosis. — Actinomycosis,  or  lumpy  jaiv,  as  it  is 
more  commonly  called,  is  primarily  a  disease  of  cattle,  al- 
though horses,  sheep,  hogs,  and  dogs  may  be  affected.  Man 
is  also  subject  to  the  disease.  The  causal  organism  is 
usually  classed  as  one  of  the  higher  bacteria.  In  the  tissues 
the  growth  is  often  in  starlike  clusters.  This  appearance 
gave  rise  to  the  name  actinomycosis.  The*term  Actinomij- 
cctcs  is  applied  to  the  group  of  which  the  organism  is  a 
member.  In  this  country  the  disease  is  not  nearly  so  wide- 
spread as  in  some  other  sections  of  the  world.  It  has  been 
found  in  about  one  out  of  sixteen  hundred  animals  killed 
in  this  country.  Tuberculosis  is  many  times  more  prevalent 
and  more  important  in  every  way ;  and  yet,  in  many  places, 
because  of  the  appearance  of  the  disease  on  the  surface  of 
the  body,  actinomycosis  has  made  more  of  an  impression  on 
the  popular  mind  than  has  tuberculosis. 

The  disease  is  not  one  that  spreads  from  animal  to  ani- 


318  AGRICULTURAL  BACTERIOLOGY 

mal,  and  hence,  like  tetanus,  can  not  be  classed  as  a  con- 
tagious disease.  It  is  believed  that  the  organism  grows  on 
certain  plants,  as  barley,  and  is  introduced  into  the  tissues 
by  the  barley  awns.  It  may  also  enter  through  a  wound 
in  the  mouth  or  through  a  hollow  tooth,  and  possibly  may 
be  inhaled.     It  is  rarely  fatal,  and  when  death  is  produced. 


Fig.  57.     Actinomycosis 

The  jaw  bone   has  become   spongy   and   a   portion  of   the   teeth   have   been   lost 

due   to  the   ravages   of   the   disease 

it  is  due  to  mechanical  causes,  such  as  the  interference  with 
breathing  or  swallowing,  or  to  the  weakening  of  a  blood- 
vessel by  the  constantly  growing  fungus. 

Symptoms. — The  first  symptom  when  the  disease  is  lo- 
cated in  the  throat,  as  is  most  common,  is  a  slight  swelling, 
which  gradually  increases  in  size  and  is  hard  and  dense. 
It  undergoes  disintegration  at  the  center,  and  may  dis- 
charge a  thick  yellow  pus.  The  opening  may  heal  over, 
only  to  break  out  again.  The  opening  by  which  the  content 
of  the  abscess  finds  its  way  to  the  outside  may  be  on  the 
surface  of  the  body  or  in  the  mouth  or  throat.  The  sore 
at  the  point  of  discharge  may  become  very  large  and  have 
the  appearance  of  a  head  of  cauliflower.  The  growth  of 
the  tumor  may  continue  for  years.     The  tongue  may  be  in- 


ACTINOMYCOSIS  319 

volved,  in  which  case  the  disease  is  often  given  the  name 
wooden  tongue.  The  organism  may  invade  the  bony  part 
of  the  jaw,  causing  it  to  become  spongy  and  enlarged.  This 
permits  the  teeth  to  become  loose,  so  that  some  of  them  may 
fall  out.  The  internal  organs  may  be  invaded  by  the  organ- 
ism. In  the  lungs,  nodules  similar  to  the  nodules  found 
in  tuberculosis  of  the  lungs  may  be  formed  under  the 
stimulus  of  the  fungus.  These  vary  in  size  from  mere 
specks  to  that  of  a  pea.  The  spleen,  liver,  and  udder  may 
contain  actinomycotic  nodules. 

The  organism  occurs  in  masses  in  the  pus  discharged 
from  the  nodules.  Because  of  the  color  of  the  organism, 
these  masses  of  growth,  which  can  be  seen  by  the  unaided 
eye,  are  often  called  sulphur  granules. 

Treatment. — The  disease  is  one  of  the  few  of  those  due 
to  the  invasion  of  the  tissues  by  a  parasitic  organism  that 
responds  to  treatment  with  drugs,  the  most  successful  of 
which  is  potassium  iodide  given  in  water  as  a  drench.  The 
dose  is  from  one  to  two  and  one-half  drams  a  day.  The 
administration  of  this  amount  of  the  drug  can  not  be  con- 
tinued for  any  length  of  time  without  producing  in  the  ani- 
mal the  effect  known  as  iodism.  This  causes  the  eyes  to 
run,  the  skin  to  become  dry  and  rough,  and  a  loss  of  appe- 
tite. When  these  evidences  of  the  drug  become  apparent, 
its  use  should  be  discontinued  for  a  few  days,  and  resumed 
later.  In  the  case  of  milch-cows,  the  milk  should  be  dis- 
carded, as  the  drug  is  excreted  through  this  channel  The 
drug  may  also  cause  abortion.  All  animals  do  not  react  fa- 
vorably to  the  drug.  Where  beneficial  results  are  obtained, 
treatment  should  be  successful  in  from  three  to  six  weeks. 
Man  does  not  acquire  the  disease  from  cattle,  but  he  be- 
comes infected  in  the  same  manner  as  cattle,  viz.,  through 
wounds  in  the  mouth.  The  meat  of  affected  animals  can  be 
used  as  food,  if  the  disease  is  localized. 


CHAPTER  XXIV 
GLANDERS  AND  TETANUS 

The  most  important  transmissible  disease  affecting,  the 
horse  and  closely  related  animals  is  glanders,  or  farcy,  as  it 
is  often  called.  The  disease  affects  primarily  horses,  mules, 
and  asses,  but  dogs  and  cats  may  acquire  it  by  feeding  on 
the  carcasses  of  glandered  animals.  The  disease  is  also 
transmissible  to  man,  and  usually  results  fatally. 

Distribution. — Glanders  is  found  in  nearly  all  parts  of 
the  world;  Australia  and  New  Zealand  are  the  only  large 
areas  of  any  importance  free  from  it.  Great  numbers  of 
horses  have  been  congregated  from  varied  sources  for  war 
purposes,  and  have  been  transported  to  other  lands,  thus 
spreading  the  disease.  It  is  asserted  that  glanders  was  in- 
troduced into  Mexico  at  the  time  of  the  Mexican  war  by 
the  American  cavalry.  During  and  after  the  Civil  War, 
the  distribution  was  very  rapid  in  this  country,  owing  to 
the  sale  of  horses  and  mules  by  the  government. 

At  the  present  time  glanders  is  most  prevalent  where 
large  numbers  of  horses  are  brought  together,  as  in  lumber 
camps,  on  the  ranges,  and  in  the  great  stables  maintained 
in  cities.  Constant  change  is  going  on  in  such  stables,  and 
every  horse  purchased  may  serve  to  introduce  the  disease, 
unless  precautions  are  taken  to  determine  the  health  of  the 
animal  before  it  is  allowed  to  come  in  contact  with  healthy 
animals.  The  number  of  horses  purchased  by  farmers  is 
comparatively  small,  and,  unless  the  farmer  buys  range 
animals,  or  those  that  have  been  in  use  by  the  large  stables, 

320 


GLANDERS 


321 


little  risk  of  acquiring  glanders  is  encountered.  Public 
stables  and  public  watering-troughs  are  undoubtedly  agents 
in  the  spread  of  the  trouble.     It  is  considered  a  wise  pre- 


Running  sores  on  a  swollen  leg  are  often  noted  with  this  disease 

After   Reynolds. 

caution  not  to  make  use  of  public  watering-troughs,  but  to 
employ  a  pail. 

Symptoms. — In  some  respects  the  disease  reminds  one  of 
tuberculosis  in  that  an  animal  may  have  it  for  a  long  time, 
and  yet  remain  in  good  flesh  and  be  able  to  stand  a  consid- 
erable amount  of  work.  In  other  words,  many  glandered 
horses  have  an  economic  value,   and  yet   are  a  constant 


322 


AGRICULTURAL  BACTERIOLOGY 


source  of  danger  to  other  animals  with  which  they  come  in 
contact.  It  is  thus  considered  wise  that  all  glandered  ani- 
mals be  destroyed,  and  that  the  owner  be  compensated  by 
the  State  for  the  protection  of  the  industry  in  general.  It 
is  through  the  purchase  of  such  chronic  cases  that  the  dis- 
ease may  be  introduced  on  the  farm. 

The  disease  primarily  affects  the  membranes  lining  the 


Fig.  59.     Glanders 
Healed  sores  on  the  nose  may  be  present  in  cases  of  chronic  glanders 

After   Reynolds. 

nasal  passages,  and  one  of  the  most  characteristic  symptoms 
is  the  discharge  of  a  sticky  fluid,  sometimes  streaked  with 
blood,  from  one  or  both  nostrils.  Small  nodules  may  form 
on  the  upper  part  of  the  nasal  septum.  The  nodules,  which 
are  translucent  and  grayish  in  color,  may  break  and  form 
ulcers,  which  destroy  the  surrounding  tissue  to  a  greater  or 
less  extent,  and  may  even  cause  a  perforation  of  the  nasal 


GLANDERS  323 

septum.  Similar  nodules  may  be  found  in  the  lungs,  and 
less  often  in  the  liver  and  kidneys. 

In  glanders  of  the  skin,  or  farcy,  nodules  are  found  in 
the  skin  and  the  underlying  tissues.  These  nodules  are 
usually  called  farcy  buds.  They  vary  in  size  from  a  hemp- 
seed  to  that  of  an  cg^.  These  nodules  break  and  form  run- 
ning sores  on  the  surface  of  the  body,  the  discharge  being 
yellow  and  sticky.  The  sores  thus  formed  often  heal  and 
leave  marked  scars  on  the  head  and  legs,  in  which  places 
they  are  most  common. 

The  acute  form  of  the  disease  is  common  in  the  mule  and 
ass,  but  is  rare  in  the  horse.  Death  often  takes  place  in 
from  two  to  four  weeks,  although  the  disease  may  become 
chronic  and  the  animal  live  for  a  number  of  years.  Treat- 
ment is  of  little  avail.  Great  precaution  should  be  exer- 
cised in  the  care  of  glandered  animals,  since  if  any  of  the 
infectious  material  is  introduced  into  the  eyes  or  nose,  or 
comes  in  contact  with  a  wound,  infection  of  the  human 
being  is  likely  to  occur.  The  manifestations  of  glanders  in 
man  are  quite  similar  to  those  noted  in  the  case  of  the  horse. 

Detection. — Glanders  is  often  easily  recognized  by  the 
characteristic  lesions  in  the  nasal  passages  or  by  the  farcy 
buds.  When  the  disease  can  not  be  recognized  by  physical 
examination,  recourse  must  be  had  to  some  other  method  of 
diagnosis.  The  most  common  method  is  to  apply  the 
mallein  test,  which  is  very  similar  to  the  tuberculin  test  in 
the  nature  and  manner  of  application.  Mallein  is  pre- 
pared by  growing  the  glanders  organism  in  glycerin  broth. 
The  culture  is  then  killed  by  heating,  and  the  dead  cells  re- 
moved by  filtration.  The  mallein  is  injected  beneath  the 
skin,  and  a  series  of  temperature  readings  is  made  both  be- 
fore and  after  the  application  of  the  mallein. 

A  few  hours  after  the  introduction  of  the  mallein  there 
appears  at  the  point  of  injection  a  swelling  which,  in  the 


324  AGRICULTURAL  BACTERIOLOGY 

glandered  horse,  is  hot  and  painful  and  continues  to  in- 
crease in  size  for  from  twenty-four  to  thirty-six  hours.  The 
swelling  persists  for  several  da3's,  disappearing  in  from 
eight  to  ten  days.  At  the  time  the  swelling  is  most  promi- 
nent, the  diseased  animal  appears  dull,  breathes  rapidly, 
and  has  a  poor  appetite.  In  the  case  of  a  healthy  horse,  the 
swelling  is  small  and  disappears  in  twenty-four  hours,  and 
no  signs  of  illness  are  ta  be  noted  following  the  injection  of 
the  mallein.  The  constitutional  reaction  in  the  diseased 
animal  is  accompanied  by  an  increase  in  the  temperature 
ranging  from  two  to  two  and  five  tenths  degrees.  The  in- 
crease begins  about  eight  hours  after  the  injection  and 
reaches  the  maximum  in  from  ten  to  fifteen  hours.  The 
fever  persists  for  from  twenty-four  to  forty-eight  hours, 
instead  of  only  a  few  hours,  as  in  the  tuberculin  test.  In 
the  healthy  horse  there  is  no  appreciable  rise  in  tempera- 
ture. 

The  test  is  not  so  accurate  a  method  of  diagnosing  glan- 
ders as  is  tuberculin  for  tuberculosis,  for  some  glandered 
horses  do  not  react  to  the  test;  but  a  positive  reaction  is 
looked  upon  as  proof  of  the  diseased  condition  of  the  animal. 
Other  tests  are  also  employed,  in  which  the  blood  is  exam- 
ined for  certain  of  the  anti-bodies  that  will  be  produced 
under  the  stimulus  of  the  glanders  bacillus.  These  meth- 
ods can  be  carried  out  only  in  the  laboratory. 

The  farmer  must  seek  to  protect  himself  by  the  purchase 
of  animals  from  known  healthy  sources,  and  by  care  in  pre- 
venting his  animals  from  coming  in  contact  with  infectious 
material  in  public  places.  The  organism  does  not  form 
spores  and  hence  is  not  especially  resistant. 

Tetanus. — Tetanus,  or  lockjaw,  is  an  example  of  a  tox- 
emia. It  is  also  an  example  of  a  disease  caused  by  a  micro- 
organism that  is  not  transmitted  from  one  animal  to  another 
under  natural  conditions.     B.  tetani  is  widely  distributed 


TETANUS  325 

in  soil,  and  is  found  in  the  large  intestine  of  horses  and 
cattle.  Heavily  manured  soils  and  those  with  a  high  con- 
tent of  organic  matter  seem  to  contain  the  bacilli  in  greater 
numbers  than  soils  lower  in  humus.  The  bacillus  is  an  an- 
aerobe that  forms  very  resistant  spores.  The  toxin  it  pro- 
duces is  one  of  the  most  poisonous  substances  known,  when  it 
is  introduced  into  the  tissues  of  an  animal.  A  man  weighing 
one  hundred  and  seventy-five  pounds  will  be  killed  by  0.23 
of  a  milligram.  Toxins  have  been  made  of  such  potency 
that  0.00,000,002  gram  is  fatal  to  a  white  mouse.  An  or- 
ganism capable  of  producing  such  a  substance  does  not  need 
to  grow  extensively  in  the  body  of  an  animal  in  order  to 
cause  injury. 

The  tetanus  bacillus  is  usually  introduced  into  the  tissues 
through  a  puncture  wound  by  some  object  that  carries  the 
infective  material  into  the  deeper  lying  tissues.  Puncture 
wounds  made  by  rusty,  dirty  nails  are  most  dangerous. 
Horses,  especially,  become  infected  in  this  manner.  Punc- 
ture wounds  bleed  but  little,  and  therefore  the  foreign  mat- 
ter is  not  likely  to  be  washed  out  by  the  blood;  nor  is  it 
easy  to  cleanse  the  wound  by  washing,  as  may  be  done  with 
a  more  superficial  abrasion.  The  infection  may  occur  in 
such  operations  as  docking,*  castration,  and  through  the 
umbilical  cord  of  foals.  The  more  frequent  occurrence  of 
the  disease  in  horses,  as  compared  to  other  domestic  animals, 
is  apparently  due  to  the  greater  susceptibility  of  the  horse 
to  the  toxin.  It  is  estimated  that  the  horse  is  twelve  times 
as  sensitive  as  the  mouse  and  360,000  times  as  sensitive  as 
the  fowl  to  this  toxin. 

In  man  a  large  proportion  of  the  disease  is  due  to  the 
wounds  produced  by  Fourth  of  July  accidents.  The  filling 
of  many  forms  of  fireworks  is  earth,  which  may  contain 
the  extremely  resistant  spores  of  the  tetanus  bacillus.  Some 
portion  of  the  filling  may  be  blown  into  the  skin  by  the 


326  AGRICULTURAL  BACTERIOLOGY 

premature  discharge  of  a  firecracker  or  some  other  form  of 
fireworks. 

Symptoms. — The  organism  grows  only  at  the  point  at 
which  it  was  introduced  into  the  tissues,  and  only  to  a  small 
extent  even  there.  In  fact,  so  little  evidence  of  its  growth 
is  shown  by  the  tissues  that  it  is  sometimes  impossible  to 
determine  the  point  of  infection.  The  organism  produces 
its  powerful  toxin,  which  is  absorbed  and  which  has  a  spe- 
cific action  on  the  nerves,  resulting  in  muscular  contractions 
in  various  parts  of  the  body.  The  tetanic  spasms  usually 
begin  in  the  muscles  of  the  head  and  neck,  extending  from 
these  parts  to  the  muscles  of  the  throat,  trunk,  and  extrem- 
ities. In  the  head,  the  muscles  of  mastication  are  first 
attacked,  giving  rise  to  the  disease  commonly  known  as 
lockjaw.  In  the  horse,  the  muscles  of  the  tail  may  be  the 
first  to  show  the  spasmodic  contractions. 

The  duration  of  the  disease  in  the  horse  may  be  a  few 
days,  or  it  may  continue  for  several  weeks.  In  cattle  the 
disease  is  usually  less  rapid,  but  rarely  runs  longer  than 
two  weeks.  Tetanus  is  usually  fatal  in  sheep,  and  about 
75  per  cent,  of  the  horses  affected  die.  In  man  the  disease 
manifests  itself  in  much  the  same  manner  as  in  the  lower 
animals.  It  was  a  very  common  disease  in  the  early  months 
of  the  Great  War.  In  certain  portions  of  the  Western 
front,  the  soil  apparently  contained  many  tetanus  bacilli. 
The  contamination  of  wounds  with  the  soil  presented  ample 
opportunity  for  the  tetanus  organism  to  enter.  Later  in  the 
struggle,  one  of  the  first  treatments  each  wounded  man  re- 
ceived was  a  dose  of  tetanus  antitoxin. 

Preventive  measures. — A  preventive  and,  to  some  extent, 
a  curative  treatment  has  been  developed  in  the  tetanus  an- 
titoxin. This  antitoxin  is  comparable  to  the  preventive 
serum  used  in  hog  cholera,  and  the  diphtheria  antitoxin- 
used  so  widely  in  human  medicine. 


TETANUS  327 

In  the  preparation  of  the  antitoxin,  it  is  necessary  to 
force  a  susceptil)le  animal,  like  the  horse,  to  produce  in  its 
blood  a  (juantity  of  the  protective  substances,  so  that  the 
blood  can  be  drawn  and  the  serum  obtained.  In  producing 
the  serum,  the  animal  is  hyper-immunized  by  the  addition 
of  repeated  doses  of  the  toxin  or  poison  produced  by  the 
organism,  beginning  with  very  minute  doses  and  gradually 
increasing  them.  This  treatment  with  constantly  increasing 
doses  of  the  toxin  is  continued  until  the  body  of  the  horse 
has  produced  a  large  quantity  of  the  substance  that  will 
neutralize  the  toxin.  Fortunately,  the  body  can  produce 
an  amount  of  the  protective  substances  in  excess  of  that 
which  is  necessary  to  render  harmless  the  toxin  introduced. 

If  some  of  the  blood  of  the  hyper-immunized  animal  is 
carried  to  an  animal  that  is  just  beginning  to  show  symp- 
toms of  tetanus,  the  antitoxin  will  be  ready  to  neutralize  the 
poison  as  it  is  formed  by  the  growth  of  the  organisms.  It 
will  tide  the  body  of  the  diseased  animal  over  the  period  of 
danger,  and  give  it  time  to  protect  itself  by  the  manufac- 
ture of  its  own  antitoxin. 

The  transfer  of  the  protective  substances  is  accomplished 
by  drawing  a  small  portion  of  the  blood,  allowing  it  to 
clot,  and  using  the  clear  serum,  which  formerly  represented 
the  commercial  product.  AVays  have  now  been  found  by 
which  the  protective  substances  can  be  concentrated  by 
chemical  means,  a  distinct  advantage,  since  it  avoids  the 
introduction  of  large  quantities  of  liquid  into  the  animal 
to  be  protected. 

The  protective  serum  is  expensive,  and  hence  is  used 
only  on  valuable  animals.  Its  widest  use  is  in  the  preven- 
tion of  the  disease  in  man.  The  immunity  thus  produced 
is  passive  and  persists  for  only  a  short  time. 


CHAPTER  XXV 
HOG  CHOLERA 

The  most  important  communicable  disease  of  hogs  is 
known  as  hog  cholera,  supposed  to  have  been  introduced 
from  Europe  in  breeding  animals.  The  first  outbreak  in 
this  country  of  which  record  exists  is  that  which  occurred 
in  Ohio  in  1833.  Since  that  time  the  disease  has  spread 
to  all  parts  of  the  country.  In  the  corn-growing  States 
the  losses  occasioned  by  it  are  enormous.  In  the  interval 
from  1894  to  1912  only  eleven  of  the  92  counties  of  Indiana 
lost  less  than  5  per  cent,  yearly  of  the  annual  hog  crop,  38 
lost  between  5  and  10  per  cent.,  30  between  10  and  15  per 
cent.,  12  between  15  and  20  per  cent.,  and  one  county  more 
than  20  per  cent.  It  is  estimated  that  85  per  cent,  of  the 
losses  incurred  in  the  hog  industry  are  due  to  this  disease. 
From  these  figures  it  is  apparent  that  hog  cholera  places 
an  enormous  tax  on  the  swine  industry  of  the  country. 

This  disease,  like  foot-and-mouth  disease,  is  one  that 
presents  high  and  low  tides.  A  widespread  outbreak  oc- 
curred in  1886-7,  another  in  1891  and  in  the  years  there- 
after, and  still  another  began  about  1911  and  continued 
for  several  years.  Its  gradual  spread  from  south  to  north 
is  shown  in  the  following  figures,  which  present  the  per- 
centage of  the  annual  hog  crop  lost  through  cholera: 

1912  1913 

Iowa IC  25.5 

Minnesota     5.5  21.4 

Nebraska    11  17.5 

South  Dakota   3.8  23.0 

North  Dakota  2  7.5 

328 


HOG  CHOLERA  329 

The  disease  is  due  to  an  ultrainicroscopic  organism  that 
{i:ains  entrance  to  the  body  by  way  of  the  digestive  tract 
or  through  the  broken  skin.  The  causal  organism  is  elim- 
inated from  the  body  in  the  feces  and  urine.  All  breeds 
of  hogs  are  susceptible  to  the  disease.  It  has  been  claimed 
by  some  that  the  mule-footed  hogs  would  not  acquire  it, 
but  experience  has  shown  this  statement  to  have  no  basis 
(»f  fact. 

Symptoms. — The/ disease  may  appear  as  a  typical  blood- 
{)oisoiiiiig  or  septicemia,  as  an  intestinal  infection,  as  a 
lung  trouble,  or  in  any  combination  of  the  three.  It  was 
formerh^  supposed  that  there  was  more  than  one  disease 
that  affected  hogs;  but,  as  methods  of  prevention  have  been 
devised,  it  has  been  found  that  all  respond  to  the  same 
treatment  and  hence  must  be  caused  by  the  same  organism. 
The  symptoms  vary  with  the  different  manifestations  of 
the  disease. 

The  first  hogs  to  die  in  any  outbreak  do  so  after  having 
shown  signs  of  illness  a  sliort  time.  It  will  usually  be 
observed  that  the  sick  hogs  fail  to  eat,  are  affected  with 
chills,  and  huddle  together  in  the  pens  to  keep  warm. 
They  stand  with  l)ack  arclied  and  with  the  hind  feet  close 
together  or  crossed.  They  sliow  stiffness  of  the  muscles 
and  joints,  and  may  stagger  and  fall  from  weakness.  The 
skin  of  ears,  nose,  abdomen,  and  that  inside  the  thighs 
may  be  reddened.  The  early  stages  are  marked  by  consti- 
pation, followed  by  a  profuse  diarrhea  in  which  tlie  feces 
have  an  offensive  odor.  If  the  lungs  are  affected,  a  hack- 
ing cough  is  noted  and  an  increased  respiration.  The  eye- 
lids are  often  stuck  together  bj'  a  purulent  discharge.  The 
temperature  is  increased,  reaching  from  104°  to  109°  F. 

If  the  attack  is  of  longer  duration,  as  in  the  chronic  form, 
there  is  more  marked  evidence  of  digestive  disturbances. 
Animals  with  chronic  cholera  become  emaciated,  the  hair 


330  AGRICULTURAL  BACTERIOLOGY 

may  drop  out,  and  even  portions  of  the  skin  may  die  and 
slough  off.  As  a  rule,  they  do  not  become  profitable  feed- 
ing animals  even  after  recovery. 

It  is  sometimes  difficult  or  impossible  to  determine  from 
the  symptoms  alone  whether  hog  cholera  is  present  in  a 


Fig.  60.     Hog  Cholera 
Hemorrhages  on  and  in  the  kidney  are  one  of  the  most  characteristic  lesions 

herd.  A  careful  post-mortem  examination  of  the  dead  an- 
imals is  necessary  in  order  to  make  a  conclusive  diagnosis. 
This  examination  should  be  made  preferably  on  the  car- 
cass of  a  sick  animal  that  has  been  killed,  or  on  one  that 
has  just  died.     If  the  examination  is  delayed  for  a  number 


HOG  CHOLERA 


331 


of  hours,  it  is  likely  to  be  of  little  service  i  i  making  a  di- 
aofiiosis  because  of  post-mortem  changes. 

Lesions. — The  extent  of  the  changes  in  the  oruans  will 
depend  on  the  length  of  the  attack.  If  the  animal  died  of 
acute  hog  cholera,  the  lesions  will  not,  as  a  rule,  be  so 
marked  as  in  the  more  chronic  form.  The  color  of  the 
skin  should  be  noted.  Red  or  purDlish  blotches  are  signi- 
ficant. The  abdominal  and  lung  cavities  should  be-  care- 
fully opened  and  the  following  organs  examined.  The 
kidneys  in  the  acute  cases  are  likely  to  be  darker  than  nor- 


Fipr.  Gl.     ITog  Cholera 
Button   ulcers  on   the  intestinal   wall   are   frequently   noted   in   cases  of  chronic 

cholera 

mal,  and  to  show  small,  red  spots  which  impart  to  the 
organ  a  "turkey-egg''  appearance.  The  spleen  or  milt  is 
usually  enlarged,  dark,  and  soft ;  the  liver  is  normal  in  ap- 
pearance ;  and  the  membranes  of  the  abdominal  cavity,  the 
stomach,  aud  the  small  intestines  may  show  red  areas,  as 
if  blood  had  been  spattered  on  them.  It  will  be  found  im- 
possible to  remove  the  blood  by  washing,  showing  it  to  be 
iu  the  tissues  rather  than  on  them.  The  hemorrhages  are 
to  be  found  in  many  different  parts  of  the  body,  and  may 
vary  in  size  from  the  pinpoint  spots  noted  in  the  kidneys  to 
areas  of  considerable  size.  The  lungs  may  or  may  not  be 
affected.     If  they   are,   the   hemorrhages  are  present   and 


332  AGRICULTURAL  BACTERIOLOGY 

portions  of  the  lung  tissue  may  be  consolidated  instead  of 
being  soft  and  filled  with  air.  The  surface  of  the  heart 
may  show  the  red  blotches.  In  the  acute  cases  the  inner 
lining  of  the  large  intestine  is  frequently  found  to  be  blood- 
stained, and  the  feces  may  be  bloody.  In  the  more  chronic 
cases  the  most  characteristic  lesions  of  the  disease  are  found 
in  the  large  -  intestine,  the  so-called  button  ulcers,  which 
are  round,  hard,  and  yellowish  with  a  dark  center.  They 
are  distinctly  raised  above  the  surrounding  healthy  surface 
of  the  intestine.  In  size  they  vary  from  a  small  point  to 
the  size  of  a  twenty-five  cent  piece.  The  finding  of  such 
ulcers  is  to  be  considered  as  a  positive  indication  of  hog 
cholera,  and  it  is  the  only  lesion  that  can  be  regarded  as 
absolutely  diagnostic. 

The  lymph-glands  in  various  parts  of  the  carcass  are 
found  upon  section  to  be  enlarged  and  reddened. 

A  number  of  causes  may  produce  symptoms  that  may  be 
mistaken  for  cholera.  Pneumonia  due  to  exposure,  dust, 
or  lung-worms  is  sometimes  confounded  with  cholera.  Im- 
proper feeding  may  cause  intestinal  disturbances.  Slops 
containing  alkalies,  such  as  soap  powders,  are  often  a 
source  of  trouble  to  garbage-fed  hogs. 

Prevention. — Since  but  little  can.be  done  to  cure  the 
disease  after  it  has  made  its  appearance  in  the  individual 
animal,  the  farmer  must  direct  his  efforts  to  the  prevention 
of  the  disease.  It  should  be  remembered  that  the  organism 
is  eliminated  from  the  body  of  the  affected  animal  in  the 
urine  and  feces,  and  that  it  is  present  in  all  the  tissues  of 
the  body.  An  animal  that  has  recovered  from  the  disease 
may  still  harbor  the  organisms  in  its  body  and  eliminate 
them.  With  these  facts  in  mind,  the  farmer  can  outline 
his  plan  for  the  protection  of  his  herd.  No  animal  should 
be  purchased  from  a  herd  in  which  cholera  has  been  present 
during  the  previous  year,  nor  from  a  herd  that  has  been 


HOG  CHOLERA  333 

subjected  to  the  preventive  treatment  in  which  the  virus 
has  been  employed  within  six  weeks.  Animals  purchased 
should  be  kept  in  quarantine  for  four  weeks  and  then  al- 
lowed to  come  in  contact  with  a  small  number  of  the  herd. 
If  these  exposed  animals  remain  healthy  after  two  or 
three  weeks'  exposure,  it  is  safe  to  place  the  purchased  an- 
imals with  the  herd.  It  is  not  essential  that  a  rigid  quar- 
antine be  established  in  the  case  of  the  purchased  animals, 
for  the  prevention  of  intimate  contact  will  usually  suffice. 
The  method  of  keeping  hogs  in  separate  houses  rather 
than  in  one  large  house  has  many  advantages,  one  being 
that  if  cholera  breaks  out  in  one  of  the  yards,  it  can  often 
be  prevented  from  spreading  to  the  remaining  sections  of 
the  herd. 

Hogs  that  have  been  shown  at  fairs  are  likely  to  be  ex- 
posed to  infection,  not  only  at  the  place  of  exhibition  but 
also  during  shipment.  Care  should  be  taken  in  allowing 
such  animals  to  mingle  with  the  herd,  until  time  has  shown 
the  animals  to  be  free  from  infection. 

The  virus  of  hog  cholera  can  be  carried  on  objects  from 
one  farm  to  another.  It  is  probable  that  this  is  one  of  the 
chief  wa3's  in  which  the  disease  progresses  in  any  locality 
into  which  it  has  been  introduced.  The  farmer  should  re- 
member that  any  object  transferred  from  an  infected  farm 
to  his  own  may  serve  to  carry  the  infection.  The  visiting 
of  the  hog-yards  in  which  an  outbreak  has  made  its  ap- 
pearance, the  transfer  of  tools  or  wagons,  or  of  animals 
such  as  dogs  or  cows,  are  ways  in  which  the  disease  spreads. 
It  seems  probable  that,  if  the  farmer  takes  care  of  those 
factors  that  he  can  control,  he  will  have  little  trouble  with 
those  he  can  not  control. 

The  herd  should  be  kept  in  as  healthy  a  condition  as 
possible  by  providing  clean,  well  ventilated  pens,  clean 
feeding-troughs,  and  proper  feed,  since  anything  that  tends 


834  AGRICULTURAL  BACTERIOLOGY 

to  weaken  the  animal  makes  it  more  likely  to  acquire  hog 
cholera  in  case  the  organisms  are  taken  into  the  body.  It 
is  generally  believed  that  the  feeding  of  new  corn  produces 
the  disease.  The  feeding  of  large  quantities  of  new  corn 
may  produce  digestive  troubles  and  make  the  animal  more 
susceptible  to  cholera,  but  it  can  not  cause  hog  cholera. 

If  cholera  makes  its  appearance  in  the  herd,  all  the 
healthy  animals  should  be  removed  at  once  to  another  field. 
One  can  not  rely  on  the  appearance  of  the  animals  to  tell 
whether  they  are  infected  or  not.  A  much  more  reliable 
way  is  to  take  the  temperature  of  each  animal,  and  to  re- 
tain all  showing  any  fever  in  the  yard  with  the  diseased 
animals.  The  normal  temperature  of  grown  animals 
ranges  from  101°  to  103°  F.  In  young  animals  the  tem- 
perature will  run  somewhat  higher,  but  in  separating  the 
herd  all  animals  having  a  temperature  of  more  than  103.5° 
should  be  considered  as  infected. 

The  carcasses  of  hogs  that  have  died  should  be  burned 
if  possible.  If  this  can  not  be  done,  they  should  be  buried 
deeply.  All  infected  litter  should  be  burned.  The  care- 
less disposal  of  carcasses  is  one  of  the  chief  ways  of  spread- 
ing and  perpetuating  the  disease. 

The  hogs  should  be  pastured  in  fields  that  do  not  border 
on  the  road  and  that  are  not  traversed  by  streams,  since 
infection  may  be  introduced  in  either  of  these  ways. 

The  most  effective  way  of  protecting  the  herd  against 
the  disease  is  to  apply  the  preventive  treatment  described 
later.  Many  cures  for  hog  cholera  have  been  proposed 
and  are  widely  advertised.  It  is  certain,  however,  that  no 
treatment  other  than  the  administering  of  the  protective 
serum  is  of  any  value. 

Protective  treatment. — A  hog  that  has  recovered  from 
a  natural  attack  acquires  an  immunity  to  the  disease,  due 
to  the  presence  in  the  blood  of  protective  substances  that 


IIOG  CHOLERA  335 

have  been  formed  under  the  stimulus  of  the  disease-pro- 
ducing organism.  The  amount  of  protective  bodies  that 
are  thus  produced  as  a  result  of  an  attack  of  the  disease 
is  not  sufficiently  great  so  that  the  blood  can  be  drawn  and 
introduced  into  the  body  of  another  animal  for  the  pur- 
pose of  imparting  immunity.  If,  however,  such  an  immune 
animal  is  injected  with  large  quantities  of  the  blood  of  a 
hog  that  is  ill  with  the  disease,  the  stimulus  imparted  by 
the  introduction,  of  the  virus  will  cause  the  animal  to  form 
additional  protective  bodies,  so  that  it  will  be  practicable 
to  draw  the  blood  and  use  it  in  protecting  other  animals. 

The  hogs  thus  treated  are  said  to  be  hyper-immunized. 
The  protective  serum  is  secured  by  bleeding  the  immunized 
hog.  This  is  done  by  cutting  off  the  tip  of  the  tail. 
About  five  or  six  cubic  centimeters  of  blood  to  one  pound 
of  body  weight  is  drawn.  This  process  is  repeated  three 
times,  at  weekly  intervals.  The  animal  is  then  given  an- 
other injection  of  the  virulent  blood,  is  then  bled  twice 
from  the  tail,  and  after  the  usual  interval  is  bled  from 
the  throat.  The  blood  is  beaten  with  a  wire  as  soon  as 
drawn  from  the  animal  to  remove  the  fibrin  and  prevent 
clotting.  One  half  of  one  per  cent,  of  carbolic  acid  is  added 
as  a  preservative. 

Before  the  serum  is  used  in  the  field  it  is  necessary  to 
determine  its  protective  power.  This  is  done  by  injecting 
varying  amounts  into  susceptible  pigs  that  are  inoculated 
at  the  same  time  with  some  virulent  blood.  In  this  manner 
it  can  be  determined  how  much  must  be  used  in  actual 
work  to  protect  an  animal.  It  will  be  seen  that  the  prepa- 
ration of  the  serum  is  expensive  because  of  the  large  num- 
ber of  hogs  that  must  be  used  and  the  labor  involved. 
Many  of  the  States  have  established  laboratories  for  the 
preparation  of  the  serum. 

By  the  use  of  the  serum  alone  a  passive  immunity  is 


336  AGRICULTURAL  BACTERIOLOGY 

produced  that  will  protect  the  animal  from  a  serious  in- 
fection for  from  six  to  ten  weeks.  If  a  small  quantity  of 
virulent  blood  is  introduced  into  the  animal  at  the  same 
time  the  serum  is  injected,  active  immunity  will  be  pro- 
duced, which  will  generally  protect  the  animal  for  life. 
The  introduction  of  the  virus  at  the  same  time  as  the  anti- 
serum may  result  occasionally  in  a  fatal  case  of  cholera. 
In  order  to  avoid  this  risk,  the  protective  serum  may  be 
injected,  and  about  a  week  or  ten  days  later  the  virus  may 
be  given,  together  with  a  second  dose  of  the  anti-serum. 
The  first  method  is  known  as  the  serum-alone  method,  the 
second  as  the  simultaneous  method,  and  the  last  as  the 
double  or  combination  method.  Each  has  its  advantages 
and  disadvantages  which  must  be  considered  in  determining 
which  to  apply.  The  serum-alone  is  safe,  but  protects  for 
only  a  short  time,  unless  the  animals  coma  in  contact  with 
infectious  material  soon  after  treatment,  in  which  case  the 
results  are  substantially  the  same  as  those  obtained  in  the 
simultaneous  treatment.  The  method  is  of  small  value  iii 
the  protection  of  breeding  animals.  It  does  allow  the 
farmer  to  protect  his  herd  for  a  short  time  when  the  dan- 
ger of  infection  is  great. 

In  the  simultaneous  method,  some  of  the  treated  animals 
may  die  froin  cholera,  because  not  sufficient  serum  was 
used  to  protect  against  the  virus  administered.  The  ani- 
mals in  which  acute  cholera  is  thus  produced  may  serve 
as  centers  of  infection  from  which  the  disease  may  spread 
to  other  herds.  This  danger  has  led  many  to  advise 
against  the  use  of  the  simultaneous  method.  In  herds  in 
which  the  disease  already  exists,  only  the  serum  should  be 
used.  The  combination  method  avoids  the  danger  of  the 
simultaneous  treatment,  since  rarely  are  any  animals  lost 
by  cholera  due  to  the  treatment.  It  is  more  expensive, 
since  serum  must  be  given  twice. 


HOG  CHOLERA  337 

Breeding  herds  should  be  protected  by  the  use  of  the 
combination  method,  even  if  cholera  is  not  present  in  the 
vicinity,  because  it  enables  the  breeder  to  send,  without 
danger,  breeding  hogs  into  infected  districts  and  to  fairs. 
Application  of  the  serum. — The  serum  may  be  applied 
by  the  farmer  liiniself,  but  if  the  virus  is  to  be  used,  as  is 
the  case  in  the  simultaneous  or  combination  methods,  a 
veterinarian  should  be  employed,  since  the  virus  is  dan- 
gerous material  and,  if  handled  by  those  who  do  not  ap- 
preciate its  nature,  trouble  may  result.  The  animals 
should  receive  a  light  laxative  diet  for  a  day  or  so  before 
being  treated,  and  should  be  kept  in  clean,  dry  quarters. 

Small  hogs  are  usually  injected  in  the  arm-pit.  The 
animal  may  be  held  on  its  back  between  two  round  fence- 
posts  joined  together  by  cleats.  Larger  animals  may  be 
snubbed  to  a  post  by  a  rope  around  the  upper  jaw,  and  the 
serum  injected  in  the  fold  of  loose  skin  at  the  side  of  the 
neck.  The  needle  of  the  hypodermic  syringe  should  be 
thrust  deep  into  the  tissue,  not  simply  through  the  skin  as 
when  tuberculin  is  applied.  If  the  infection  of  the  animal 
with  organisms  that  will  cause  inflammation  and  abscesses 
is  to  be  avoided,  it  is  necessary  to  see  that  the  syringe  is 
sterilized  before  use,  by  placing  it  in  cold  water  and  bring- 
ing it  to  the  boiling-point.  If  the  syringe  has  leather 
washers  on  the  plunger,  its  sterilization  must  be  accom- 
plished by  the  use  of  chemical  disinfectants,  since  boiling 
would  destroy  the  leather.  The  skin  at  the  point  where 
the  injection  is  to  -be  made  should  be  scrubbed  with  a  stiff 
brush,  warm  water,  and  soap ;  then  rinsed  with  some  water 
that  has  been  boiled  and  allowed  to  cool.  The  skin  is  then 
treated  with  a  4  per  cent,  solution  of  carbolic  acid  or  tinc- 
ture of  iodine.  Care  should  be  exercised  to  keep  everything 
clean  during  the  process. 

The  doses  of  serum  are  as  follows : 


338  AGRICULTURAL  BACTERIOLOGY 


^eight  of  animal 

When  virus  is  used 

No  virus 

0-20     lbs. 

15  cc 

10  cc. 

20-50     lbs. 

25  cc. 

20  cc. 

50-75     lbs. 

35  cc. 

25  cc. 

75-100  lbs. 

40  cc. 

30  cc. 

100-150  lbs. 

50  cc. 

35  cc. 

150-200  lbs. 

55  cc. 

40  cc. 

200-300  lbs. 

65  cc. 

45  cc. 

300-400  lbs. 

85  cc. 

65  cc. 

400^000  lbs. 

100  cc. 

85  cc. 

The  larger  quantity  of  serum  is  used  with  the  virus  in 
order  to  protect  the  animal  against  the  v-irus,  which  by 
itself  would  cause  death.  The  virus  is  usually  applied  at 
some  other  point  than  the  serum,  as  beneath  the  skin  at  the 
center  of  the  space  between  the  fore  legs  when  the  serum  is 
applied  in  the  arm-pit. 

For  a  few  days  after  the  serum  is  administered  the  feed 
should  be  reduced  to  about  one  half  the  normal  amount, 
gradually  increasing  until  at  the  fourth  week  the  full  feed 
may  be  given.  When  only  the  serum  is  given,  there  should 
be  little  or  no  reaction.  With  the  double  or  the  simul- 
taneous treatment  in  six  to  ten  days  after  the  injection, 
the  reaction  fever  sets  in  and  the  temperature  may  rise  to 
106°  F.  The  animals  may  lose  appetite,  have  chills,  and 
present  the  symptoms  of  a  mild  case  of  hog  cholera.  The 
more  susceptible  animals  may  die  from  the  effects  of  the 
virus.  The  hogs  that  show  symptoms  may  eliminate  the 
virus,  and  be  the  starting-point  of  an  outbreak  of  cholera 
in  case  they  come  in  contact  with  susceptible  animals. 

The  results  that  have  been  obtained  with  the  serum  have 
been  such  as  to  recommend  its  use.  When  applied  in  herds 
in  which  the  disease  had  already  made  its  appearance,  more 
than  80  per  cent,  of  the  animals  were  saved,  while  the 
treatment  applied  before  the  infection  of  the  herd  took 
place  has  protected  more  than  90  per  cent,  of  the  animals 
against  infection. 


HOG  CHOLERA  339 

There  seems  to  be  little  doubt  but  that  any  farmer  or 
breeder  can  protect  his  herd  against  loss  from  cholera  by  the 
consistent  and  careful  use  of  the  protective  serum  and  the 
virus  of  the  disease.  It  is  a  matter  of  some  expense,  and 
the  farmer  must  weigh  the  cost  of  the  insurance  against  the 
probable  loss  from  cholera  before  deciding  whether  or  not 
to  apply  the  treatment. 


CHAPTER  XXVI 
DISEASES  OF  FOWLS 

The  transmissible  diseases  of  fowls  inflict  a  heavy  tax  on 
the  poultry-raiser  and  the  general  farmer.  Present  knowl- 
edge concerning  many  of  these  diseases  is  far  from  com- 
plete, and  in  many  cases  so  fragmentary  that  no  definite 
plan  for  the  eradication  and  prevention  can  be  devised 
other  than  the  customary  plan  applicable  in  most  cases  of 
transmissible  diseases,  viz.,  removal  of  affected  individuals, 
'destruction  of  carcasses,  and  general  cleanliness  and  dis- 
infection. 

Chicken  cholera. — Chickens,  like  swine,  are  subject  to 
dietary  disorders  which  may  often  simulate  a  true  con- 
tagious disease  in  the  rapidity  with  which  it  appears  in  the 
flock  and  in  its  high  mortalit}^  Cholera  is  a  term  applied 
to  many  of  such  disorders  that  are  not  produced  by  a  spe- 
cific organism.  The  true  chicken  cholera  is  rare  in  this 
country,  and  is  due  to  the  invasion  of  the  body  by  a  spe- 
cific form  of  bacteria. 

Symptoms. — The' urates,  that  part  of  the  excrement  ex- 
creted by  the  kidneys,  in  the  case  of  healthy  birds  are  pure 
white  in  color.  In  birds  affected  with  cholera  the  urates 
are  yellow,  often  a  bright  yellow,  and  sometimes  a  bright 
green.  This  change  in  color  is  not  proof  of  the  presence 
of  cholera,  but  is  a  valuable  indication  of  the  disease. 
Diarrhea  is  usually  present.  The  sick  bird  leaves  the  flock, 
becomes  weak  and  drowsy,  acts  dumpish,  and  the  feathers 
are  roughened.  Intense  thirst  is  noted,  the  appetite  is 
poor,  and  the  crop  remains  distended  with  food.     There  is 

340 


CHOLERA  341 

a  rapid  loss  of  flesh.  The  disease  makes  rapid  progress  in 
the  flock,  because  of  the  short  period  of  incubation,  from 
one  to  three  days.  Most  of  the  affected  birds  die  in  a  short 
time  of  an  acute  form  of  the  disease;  others  may  have  a 
chronic  type;  recovery  is  rare. 

On  post-mortem  examination  the  digestive  organs  will  be 
found  to  be  inflamed,  and  the  liver  is  usually  enlarged  and 
softened.  The  presence  of  cholera  can,  however,  be  estab- 
lished only  by  a  bacteriological  examination  of  the  blood, 
which  will  be  found  to  contain  great  numbers  of  the  causal 
organisms.  The  disease  is  a  true  septicemia.  The  organ- 
ism enters  the  body  by  the  ingestion  of  contaminated  food 
or  water,  which  may  become  contaminated  with  the  excre- 
ment of  the  affected  birds  or  the  material  that  drops  from 
the  beak.  The  extensive  lesions  in  the  intestine  allow  the 
excrement  to  become  mixed  with  manure. 

The  disease  may  be  introduced  into  the  flock  by  the  pur- 
chase of  a  bird  with  a  chronic  form  of  the  disease,  or  by 
doves  and  wild  birds  that  fly  from  farm  to  farm. 

Prevention. — Nothing  can  be  done  for  the  birds  that  are 
infected.  All  efforts  must  be  concentrated  in  preventing 
the  spread  of  the  disease.  It  should  be  remembered  that 
every  drop  of  blood  contains  great  numbers  of  the  causal 
organisms,  and  that  if  any  portion  of  the  carcass  is  con- 
sumed by  well  birds,  they  are  certain  to  become  infected. 
It  is  advisable  to  kill  the  birds  that  show  any  symptoms  of 
disease.  Tliis  should  be  done  in  such  a  way  that  no  blood 
is  drawn.  The  dead  fowls  should  be  promptly  disposed 
of;  the  feed  and  water  troughs  should  be  thoroughly  disin- 
fected, as  also  the  roosting  houses.  If  possible,  the  still 
healthy  birds  should  be  removed  to  fresh,  uncontaminated 
grounds.  The  causal  organism  does  not  produce  spores  and 
will  not  persist  long  outside  the  body  of  the  bird.  It  is 
considered  safe  to  bring  new  stock  on  the  place  after  the 


342  AGRICULTURAL  BACTERIOLOGY 

expiration  of  two  weeks,  provided  the  house  and  other  con- 
taminated objects  have  been  thoroughly  disinfected. 

Fowl  typhoid. — This  disease  is  often  mistaken  for 
chicken  cholera.  It  is,  however,  produced  by  a  different 
organism.  The  disease  is  less  rapid  in  its  progress  in  the 
individual  bird  than  is  cholera.  The  diarrhea  so  character- 
istic of  cholera  is  absent,  and  the  intestines  are  pale  in- 
stead of  deep  red,  as  in  cholera;  the  contents  are  normal 
in  consistency,  while  in  cholera  the  intestinal  contents  are 
liquid  and  blood-stained.  The  blood  is  free  from  the  or- 
ganisms. It  is  not  especially  important  that  a  correct  diag- 
nosis be  made  as  to  which  of  these  diseases  is  present  in 
the  flock,  since  identical  methods  of  prevention  should  be 
employed  with  either.  Cleanliness  should  be  the  chief  re- 
liance of  the  poultryman  against  these  diseases. 

Roup. — Roup,  or  diphtheria  of  fowls,  is  considered  the 
most  important  transmissible  disease  affecting  the  barn- 
yard fowl  of  this  country.  It  occurs  in  turkeys,  ducks, 
pigeons,  and  pheasants,  as  well  as  chickens.  The  cause  of 
roup  has  not  been  discovered,  and  it  is  not  certain  whether 
chickenpox  and  canker  are  different  diseases  from  roup 
or  different  manifestations  of  the  same  disease. 

It  has  sometimes  been  considered  that  this  disease  has 
some  relation  to  diphtheria  in  man.  There  is  no  reason 
for  such  belief  other  than  that  in  certain  forms  of  roup 
there  may  be  formed  a  membrane  similar  to  the  membrane 
noted  in  diphtheria.  The  first  symptom  of  roup  is  a 
watery  discharge  from  the  nostrils  and  often  from  the  eyes. 
The  bird  becomes  dumpish;  the  breathing  is  often  noisy, 
due  to  the  obstruction  of  the  air-passages  by  the  exudate. 
The  fowl  may  be  able  to  breathe  only  by  opening  the  beak. 
Sneezing  is  frequent.  The  eyes  may  be  covered  with  a  dry 
discharge,  or  they  may  be  forced  from  the  sockets  by  the 
accumulation  of  cheesy  matter  in  the  sockets.     There  may 


ROUP  343 

be  found  in  the  mouth  and  throat  patches  of  grayish-yellow 
exudate  or  membranes.  Death  is  often  occasioned  throu«;h 
suffocation  due  to  the  closing  of  the  throat  by  the  mem- 
brane. The  swelling  of  the  head  caused  by  the  accumula- 
tion of  the  exudate  in  the  various  cavities  of  the  head  has 
given  rise  to  the  term  swell-head. 
It  is  considered  that  potassium  permanganate  is  helpful 


i(T.  62.     Roup 
The  eye  is  swollen  and  filled  with  exudate  as  is  the  mouth 

both  as  a  preventive  and  for  the  treatment  of  affected  birds. 
It  may  be  added  to  the  drinking  water  in  sufficient  quanti- 
ties to  impart  a  pink  color  to  the  water.  The  heads  of  the 
affected  birds  may  be  dipped  in  a  1  or  2  per  cent,  solution 
of  the  same  substance. 

Roup  is  to  be  differentiated  from  simple  catarrh,  which 
closely  resembles  the  human  trouble  known  as  cold-in-the- 
head.  Simple  catarrh  is  caused  by  exposure  to  dampness, 
cold  winds,  and  by  improper  ventilation  of  the  houses.     It 


344  AGRICULTURAL  BACTERIOLOGY 

has  been  shown  experimentally  that  it  is  impossible  to  pro- 
duce roup  in  these  ways.  There  seems  to  be  no  doubt,  how- 
ever, that  birds  suffering  from  catarrh  are  susceptible  to 
roup. 

Roup  may  be  carried  from  flock  to  flock  by  the  transfer 
of  birds  with  a  mild  form  of  disease.  Fowls  should  not  be 
purchased  from  infected  flocks,  and  it  is  well  to  place  in 
quarantine  for  some  days  new  birds  or  those  that  have  been 
at  shows  before  i)lacing  them  with  the  flock.  Any  bird 
showing  any  discharge  from  the  mouth  or  eyes  should  be 
removed  at  once  from  the  flock. 

White  diarrhea. — Of  the  diseases  affecting  young  chicksy 
white  diarrhea  is  the  most  important.  It  is  probable  that 
more  than  one  trouble  has  been  classed  under  this  name. 
The  white  diarrhea  of  young  chicks,  caused  by  B.  pullorum, 
is  the  most  important.  This  disease  offers  an  example  of 
hereditary  transmission  of  disease.  It  has  been  shown  that 
the  ovaries  of  the  hen  may  be  affected,  and  that  the  ova 
contain  the  organism.  The  young  chick  becomes  infected 
from  the  yolk  sac.  Some  of  the  females  that  survive  con- 
tinue to  harbor  the  germ  and  become  bacillus-carriers.  The 
adult  females  may  become  infected  by  contact  with  other 
infected  adults  or  by  infected  litter.  They  may  then  be- 
come bacillus-carriers.  The  infection  is  in  all  probability 
acquired  through  the  mouth. 

The  economic  importance  of  the  disease  is  occasioned  by 
its  effect  on  young  chicks.  The  greatest  danger  of  infec- 
tion is  during  the  first  forty-eight  hours.  The  danger  of 
infection  is  very  slight  after  four  days. 

The  affected  chicks  appear  stupid  and  remain  under  the 
hover  or  hen  much  of  the  time.  The  feathers  become  rough, 
and  the  wings  droop.  There  is  constant  loss  of  weight. 
The  chicks  eat  little  and  appear  unable  to  pick  up  their 
food.     A  whitish  discharge  from  the  vent  soon  makes  its 


WHITE  DIARRHEA  345 

appearance.  The  discharge  may  be  creamy  or  sometimes 
mixed  with  brown,  and  it  is  more  or  less  sticky  or  glairy. 
In  many  cases  it  clings  so  closely  to  the  down  as  to  close 
up  the  vent.  ]\Iany  of  the  chicks  peep  constantly  or  utter 
a  shrill  cry,  apparently  of  pain,  when  attempting  to  void 
the  excrement.  The  abdomen  is  enlarged  and  protrudes 
to  the  rear.  The  post-mortem  examination  shows  no 
marked  lesions.  The  organs  are  all  pale;  the  alimentary 
tract  is  usually  empty  except  for  some  slimy  fluid. 

The  prevention  of  the  disease  must  rest  on  the  non-intro- 
duction of  bacillus-carriers  in  the  purchase  of  breeding 
stock,  and  by  the  purchase  of  eggs  and  young  chicks  from 
flocks  that  are  known  to  be  free  from  the  disease.  The 
w^idespread  infection  of  breeding  birds  is  shown  by  the 
fact  that,  in  a  flock  in  which  the  losses  of  the  young  chicks 
had  been  excessive,  more  than  80  per  cent,  of  the  laying 
hens  were  shown  to  have  diseased  ovaries.  The  chicks  that 
recover  from  the  infection  do  not,  as  a  rule,  grow  as  rapidly 
as  do  non-infected  birds. 

It  has  been  shown  conclusively  that  the  feeding  of  sour 
milk  to  young  chicks  is  of  value  in  preventing  the  spread  of 
the  disease.  The  dishes  in  which  the  milk,  is  kept  should 
be  cleaned  daily  and  a  fresh  supply  of  milk  provided. 

The  incubators  and  brooders  should  be  thoroughly  dis- 
infected after  each  hatch,  and  extreme  cleanliness  should 
be  practised  in  all  regards  in  the  handling  of  young  chicks. 


CHAPTER  XXVII 
BACTERIAL  DISEASES  OF  PLANTS 

The  most  important  transmissible  diseases  of  animals  are 
those  caused  by  bacteria  rather  than  by  the  other  groups 
of  microorganisms  such  as  molds  and  yeasts,  while  in  the 
plant  kingdom  the  reverse  is  true.  The  molds  are  by  na- 
ture better  fitted  to  penetrate  into  the  tissues  of  the  plant 
than  are  the  bacteria. 

Just  as  the  increased  commerce  in  animals  has  hastened 
and  accentuated  the  spread  of  the  transmissible  diseases  of 
animals,  the  increased  sale  of  seeds  and  plants  of  all  kinds 
and  their  shipment  from  one  part  of  the  country  to  another 
has  led  to  the  rapid  spread  of  both  bacterial  and  fungus 
plant  diseases.  At  the  present  time  about  forty  bacterial 
diseases  of  plants  have  been  described.  A  few  are  wide- 
spread and  are  certain  to  come  to  the  notice  of  every  one 
engaged  in  farming,  and  are  of  great  economic  importance. 

The  bacterial  diseases  of  plants  may  be  divided  into  four 
classes,  depending  on  the  manner  in  which  they  affect  the 
plant:  the  blights,  the  rots,  the  wilts,  and  the  galls.  In 
the  first  the  tissue  is  killed  by  the  organism,  but  it  is  not 
decomposed  as  in  the  rots,  in  which  the  tissue  is  not  only 
killed  but  decomposed;  while  in  the  wilts  the  passage  of 
water  to  some  portion  of  the  plant  is  interfered  with,  and 
hence  death  of  the  affected  tissues  soon  ensues. 

The  complicated  questions  that  arise  in  connection  with 
the  immunity  against  bacterial  diseases  of  animals  do  not 
occur  in  the  bacterial  diseases  of  plants.  There  is  a  dift'er- 
ence  in  the  susceptibility  of  different  plants  to  the  same 

346 


PEAR  BLIGHT  347 

organism.  Efforts  are  being  made  to  increase  and  extend 
this  natural  immunity.  Much  more  can  be  done  in  an  ex- 
perimental way  in  the  breeding  of  resistant  varieties  of 
plants  than  can  be  done  with  animals. 

Pear  blight.— The  most  important  of  the  blights  is  that 
which  affects  the  pear  and  apple,  and  to  a  lesser  extent  the 
quince,  apricot,  and  plum.  It  was  first  observed  in  1780 
in  the  Hudson  River  valley,  and  as  orcharding  has  spread 


Fior.  63.     Pear  Blight 

Normal   fruit   is  shown   on   the   right  and   diseased  fruit  on   the   left.     In   the 

center  one  of  tl*  i)ear8  is  healthy,  the  other  is  affected 

westward,  the  disease  has  developed,  until  it  is  now  found  in 
all  parts  of  this  country  and  Canada.  In  Colorado  it  found 
such  favorable  conditions  that  it  has  caused  the  abandon- 
ment of  commercial  pear-growing.  It  has  also  caused  great 
losses  in  California.  As  far  as  our  present  knowledge  goes, 
the  blight  is  of  American  origin  and  is  confined  to  North 
America. 

Th^  disease  is  readily  recognized  by  the'  fact  that  the 
young  twigs  appear  to  have  been  injured  by  fire.  This 
condition  has  given  rise  to  the  common  name  of  fire  blight. 
The  leaves  of  the  affected  parts  turn  brown  or  black,  and 


348  AGRICULTURAL  BACTERIOLOGY 

cling  to  the  diseased  twigs  long  after  the  other  leaves  have 
fallen.  The  twigs  show  a  blackened  and  shriveled  bark. 
The  bacteria  enter  the  tissues  through  the  blossoms,  being 
carried  from  flower  to  flower  by  bees  and  other  insects. 
The  immature  fruit  shows  the  disease  by  turning  dark  and 
gradually  drying  up.  From  the  flowers  the  germs  find 
their  way  into  the  cambium,  or  growing  layer  immediately 
below  the  bark.  The  diseased  condition  develops  backward 
in  the  twig  at  the  rate  of  an  inch  or  more  a  day.  The 
blackening  of  the  bark  does  not  occur  as  fast  as  the  infec- 
tion spreads,  so  that  infected  tissue  is  always  found  sev- 
eral inches  in  advance  of  any  outward  signs.  As  the  sea- 
son progresses  the  tissue  becomes  harder  and  less  favorable 
for  the  growth  of  the  organism,  and  b}^  the  middle  of  the 
summer  the  progress  of  the  disease  has  ceased. 

The  infection  may  also  occur  through  wounds  in  older 
tissue.  It  often  reaches  the  large  limbs  and  even  the  trunk, 
in  which  case  it  is  known  as  body  blight.  The  bacteria  pass 
the  winter  in  the  blighted  parts.  These  hold-over  bacteria 
become  active  with  the  increased  sap  flow  in  the  spring, 
and  soon  spread  to  the  healthy  bark,  where  they  multiply 
so  rapidly  that  at  the  time  the  blossoms  open  the  bacterial 
growth  oozes  from  the  cracks  in  the  diseased  bark.  In- 
sects attracted  to  this  material  become  contaminated  and 
thus  carry  the  organisms  to  the  blossoms.  The  bacteria 
multiply  rapidly  in  the  nectar  of  the  flowers,  and  thus  in- 
fection is  carried  from  the  old  wood  to  the  new.  It  is  not 
rare  to  see  a  tree  with  almost  every  new  twig  showing  symp- 
toms of  the  disease  through  its  blackened  leaves. 

Since  the  bacteria  are  protected  by  the  bark,  nothing  can 
be  applied  to  the  tree  that  will  destroy  the  organisms ;  hence 
this  trouble  does  not  lend  itself  to  such  treatments  as  are 
found  efl'ective  in  combating  fungous  diseases,  in  which  the 
causal  organism  is  found  on  the  surface  of  the  plant.     The 


CABBAGE  ROT  349 

only  known  method  of  control  is  by  the  removal  of  all  dis- 
eased branches  as  the  symptoms  appear.  The  cut  should 
be  made  twelve  to  fifteen  inches  below  the  last  visible  sign 
of  the  disease.  The  diseased  wood  should  be  burned.  Care 
should  be  exercised  not  to  spread  the  infection  through  the 
prnninf>-kiiife  or  saw. 

Cabbage  rot. — Of  the  class  of  bacterial  diseases  known  as 
the  rots,  the  black  rot  of  the  cabbage  and  related  plant??  is 
most  common  ami  important.  The  first  s^^mptom  is  the 
appearance  of  yellow  or  brown  areas  near  the  margin  of  the 
leaf.  The  organism  enters  the  tissues  through  the  water 
pores  on  the  edge  of  the  leaf,  and  spreads  along  the  ribs  of 
the  leaf,  ultimately  reaching  the  main  stem  of  the  plant  in 
many  cases.  It  causes  the  death  and  softening  of  the  tis- 
sues. Invasion  by  other  forms  readily  occurs  in  the 
broken-down  tissue,  with  the  result  that  the  entire  head 
ultimately  is  destroyed.  The  affected  ribs  are  blackened, 
and  on  cutting  across  the  infected  stem  one  can  see  the 
blackened  ends  of  the  fibrous  strands  (the  fibro-vascular 
bundles). 

The  organisms  may  also  enter  the  plant  through  wounds 
on  the  roots,  such  as  are  made  when  the  young  plants  are 
transplanted.  It  has  been  shown  that  the  organisms  may  be 
on  the  seed,  and  thus  the  soil  of  the  seed-bed  infected  with 
the  organisms,  which  await  a  favorable  opportunity  to  pene- 
trate the  plant. 

Preventive  measures  must  consist  of  disinfection  of  the 
seed  and  rotation  of  crops. 

Rots  caused  by  other  bacteria  occur  in  carrots,  sugar- 
beets,  muskmelons,  and  hyacinths. 

Wilts. — The  wilts  of  the  cucumber,  muskmelon,  squash, 
and  pumpkin  are  widespread  in  the  eastern  half  of  the 
United  States.  The  disease  is  characterized  by  a  wilting 
of  the  vine,  without  any  visible  external  cause.     The  leaves 


350  AGRICULTURAL  BACTERIOLOGY 

and  runners  wilt  suddenly,  as  if  from  a  lack  of  water  or 
from  too  hot  a  sun.  The  whole  plant  may  wilt,  or  only 
one  runner.  The  disease  is  caused  by  an  orojanism,  the 
growth  of  which  fills  the  water-ducts  with  a  viscid  mate- 
rial that  prevents  the  rise  of  the  water,  and  wilting  follows. 
If  the  cut  ends  of  a  vine  are  rubbed  together  gently  and 
drawn  apart  slowly,  the  viscid  matter  will  string  out  for 
some  distance. 

The  infection  is  supposed  to  occur  through  wounds  in- 
flicted by  insects,  such  as  the  striped  cucumber-beetle  and 
the  common  squash-bug. 

A  similar  wilt  affects  the  egg-plant,  tomato,  Irish  potato, 
and  tobacco. 

Galls  or  tumors. — Another  class  of  plant  diseases  is 
marked  by  the  formation  of  galls  and  tumors.  Crown  gall 
is  the  most  important,  and  is  peculiar  by  reason  of  the 
great  number  of  plants  that  are  susceptible  to  the  attacks  of 
the  organism.  The  apple,  peach,  plum,  prune,  apricot, 
cherry,  grape,  raspberry,  blackberry,  rose,  English  walnut, 
chestnut,  almond,  white  poplar,  hop,  sugar-beet,  potato,  to- 
mato, tobacco  and  Paris  daisy  are  susceptible.  The  great- 
est economic  losses  are  in  connection  with  fruit  trees  and 
shrubs.  It  has  also  attracted  attention  because  some  of  the 
manifestations  of  the  disease  are  very  similar  to  cancer  in 
human  beings.  The  presence  of  the  causal  organism  stimu- 
lates the  surrounding  plant  tissue  to  continued  and  persist- 
ent growth,  which  results  in  the  formation  of  excrescences 
or  tumors  of  varying  size. 


CHAPTER  XXVIII 
DISINFECTION 

In  the  discussion  of  various  diseases,  it  has  been  shown 
that  there  are  a  number  of  ways  by  which  the  causal  or- 
ganisms are  eliminated  from  the  body  of  the  diseased  ani- 
mal. For  each  disease  the  manner  of  elimination  is  more 
or  less  characteristic.  In  some  it  is  true  that  the  organisms 
ma}'  be  discharged  in  a  number  of  ways,  as  in  the  case  of 
tuberculosis,  in  which  the  organisms  are  to  be  found  in  the 
sputum,  the  feces,  the  milk  when  the  udder  is  involved,  and 
in  the  discharge  from  the  genital  passages  when  the  repro- 
ductive organs  are  affected.  In  the  case  of  Texas  fever  the 
causal  organism  is  able  to  leave  the  body  only  as  the  blood 
is  drawn,  and  under  natural  conditions  the  transmission  of 
the  organism  from  animal  to  animal  is  due  entirely  to  the 
bite  of  a  specific  insect,  one  of  the  cattle  ticks. 

It  has  also  been  shown  that  the  organisms  vary  greatly 
in  their  resistance  to  environment.  Those  that  produce 
spores  are,  as  a  rule,  resistant  to  all  agencies,  and  persist 
for  long  periods  outside"  the  body  in  the  dormant  form. 
The  non-spore-forming  organisms  differ  greatly  in  resist- 
ance, some  resisting  certain  agencies  almost  as  long  as  the 
spore-bearing  organisms,  while  others  are  so  sensitive  that 
the  disease  produced  by  them  can  be  transmitted  from  ani- 
mal to  animal  only  by  the  most  intimate  contact.  It  is 
fortunate  that  none  of  the  important  transmissible  diseases 
in  man  is  due  to  spore-bearing  organisms,  and  but  two  of 
the  diseases  affecting  animals,  viz.,  anthrax  and  blackleg. 
If  it  were  otherwise,  the  difficulties  in  combating  the  trans- 
missible diseases  would  be  greatly  increased. 

351 


352  AGRICULTURAL  BACTERIOLOGY 

The  control  of  infectious  diseases  rests  on  the  prevention 
of  the  passage  of  the  causal  organism  from  diseased  to 
healthy  animals.  This  is  accomplished  in  part  by  the  iso- 
lation of  diseased  animals,  thus  preventing  contact  with 
non-infected  animals.  The  federal  and  State  quarantines, 
and  those  established  by  other  agencies,  seek  to  prevent  the 
spread  of  disease  in  this  v^ay.  Another  phase  in  the  pre- 
vention of  disease  is  the  destruction  of  the  organisms  in 
the  material  discharged  from  the  body  of  the  affected  ani- 
mal by  the  use  of  some  physical  or  chemical  agent  before 
any  healthy  animal  has  opportunity  to  come  in  contact 
with  the  infectious  material.  This  method  is  being  used 
with  the  greatest  success  in  the  prevention  of  human  dis- 
eases. It  is  evident  that,  before  it  can  be  applied,  definite 
knowledge  must  be  obtained  of  the  nature  and  resistant 
powers  of  the  organism,  and  the  ways  in  which  it  is  elimi- 
nated from  the  body;  otherwise  all  efforts  are  likely  to  be 
unsuccessful,  for,  to  secure  effective  results,  every  organism 
must  be  destroyed. 

In  the  case  of  typhoid  fever  it  is  easy  to  treat  all  of  the 
infectious  discharges  of  the  patient  so  as  to  prevent  the 
spread  of  the  disease.  Indeed,  the  concurrent  disinfection 
or  the  immediate  treatment  of  all  infectious  material  as 
soon  as  it  leaves  the  body  of  the  patient  is  so  successful  that 
practically  all  of  the  transmissible  diseases  of  man  are  now 
treated  in  the  same  wards  in  some  of  the  great  hospitals  of 
the  world,  without  the  various  diseases  spreading  from  one 
patient  to  another.  The  former  plan  was  to  pay  little  at- 
tention to  the  treatment  of  the  discharges,  but  to  attempt  to 
destroy  the  organisms  in  the  room  and  on  the  objects  with 
which  the  patient  had  been  in  contact  after  death  or  recov- 
ery had  taken  place.  This  is  called  terminal  disinfection, 
and  represents  that  which  must  be  employed  in  the  control 
of  animal  diseases,  together  with  isolation  of  the  affected 


DISINFECTION  353 

animals.  In  other  words,  the  farmer  will  find  it  necessary 
to  destroy  the  disease-producing:  organisms  in  the  stables 
in  which  diseased  animals  have  been  quartered  before  the 
stables  are  used  for  healthy  stock. 

Natural  agencies. — The  two  agencies  of  nature  that  de- 
stroy many  disease-producing  organisms  are  drying  and 
light.  The  disease-producing  organisms  vary  widely  in 
their  resistance  to  desiccation.  Most  of  the  non-spore-pro- 
ducing types  endure  drying  for  only  a  short  time,  and  it  is 
certain  that  this  is  one  of  nature's  most  effective  ways  of 
destro3'ing  and  limiting  the  spread  of  harmful  organisms. 

The  direct  rays  of  the  sun  exert  a  powerful  germicidal 
effect,  and  are  able  within  a  comparatively  short  time  to 
destroy  not  only  the  vegetative  cells  of  the  organisms  but 
many  of  the  spores.  The  action  of  light  as  a  purifying 
agent  is,  however,  often  overestimated.  It  is  effective  only 
when  the  direct  rays  of  the  sun  strike  the  unprotected  or- 
ganism. The  action  of  diffuse  daylight  is  so  small  as  to 
have  no  practical  importance,  and  when  the  organisms  are 
covered  with  a  layer  of  dust,  or  are  embedded  in  manure  or 
other  material,  the  action  of  sunlight  is  of  no  importance. 

It  is  certain  that  ample  provision  should  be  made  for 
light  in  our  houses  and  stables,  but  not  with  the  idea  that 
disease-producing  organisms  shall  be  destroyed,  but  rather 
to  render  ourselves  and  our  domestic  animals  more  resistant 
in  case  they  are  brought  in  contact  with  infectious  material. 

Heat  is  another  physical  agent  that  can  be  used  in  the 
destruction  of  organisms.  It  is  applied  either  in  the  form 
of  dry  heat,  or  as  steam  or  hot  water,  depending  on  the 
material  to  be  treated.  Here  again  the  resistant  powers 
of  the  organism  must  be  considered  in  determining  the  ex- 
posure that  must  be  used  to  be  effective.  All  small  objects 
of  wood  or  iron,  and  all  clothing,  can  be  most  easily  ren- 
dered harmless  by  boiling.     In  the  control  of  the  trans- 


354  AGRICULTURAL  BACTERIOLOGY 

missible  disease  of  human  beings,  this  process  is  of  the  great- 
est importance.  The  use  of  dry  heat  is  limited,  except  when 
material  is  to  be  destroyed  by  burning,  a  method  that  should 
be  widely  used  in  the  disposal  of  carcasses  of  animals  and 
litter. 

Chemical  disinfectants. — A  large  number  of  chemicals 
have   an   injurious   action   on   microorganisms.     It   is  cus- 
tomary to  divide  them  into  two  classes,  which  differ  in  the 
intensity   of   action.     Those   that   have   a   relatively   weak 
action  and  tend  to  prevent  the  growth  of  organisms  rather 
than  to  destroy  them  are  termed  antiseptics,  or  preserva- 
tives when  used  in  foods.     Those  that  have  a  more  pro- 
nounced action  and  destroy  the  organisms  are  called  dis- 
infectants.    It  will  be  apparent  that  when  a  disinfectant  is 
present  in  small  amounts,  it  will  have  an  antiseptic  action, 
since  cessation  of  growth  will  always  precede  death  of  the 
organism ;  but  certain  of  the  antiseptics  can  not  exert  a  dis- 
infecting action,  even  if  used  in  concentrated  form.     For 
example,  boric  acid  is  but  slightly  soluble  in  water,  and  in  a 
saturated  solution  exerts  an  antiseptic  action;  but,  owing 
to  its  limited  solubility,  it  can  never  be  classed  as  a  disin- 
fectant.    Some  of  the  disinfectants  have  the  power  of  over- 
coming  offensive   odors   by   combining   with   specific    sub- 
stances, and  are  often  called  deodorants.     Some  deodorants 
have  little  or  no  disinfecting  action,  and  of  course  are  of 
little  or  no  value,  since  they  do  not  act  on  the  source  of 
the  trouble.     Again,  some  chemicals  used  as  disinfectants 
have  an  injurious  action  on  insects,  such  as  lice  on  animals. 
In  the  use  of  these  agents  the  farmer  should  first  have  in 
mind  what  he  desires  to  accomplish,  and  then  choose  the 
agent  that  is  most  likely  to  be  effective  as  a  disinfectant,  a 
deodorant,  or  an  insecticide.     He  must  also  have  informa- 
tion as  to  the  resisting  power  of  the  organisms  he  is  attempt- 
ing to  kill,  and  as  to  the  effectiveness  of  the  disinfecting 


DISINFECTION  355 

agent,  otherwise  his  work  is  likely  to  be  of  no  avail.  For 
example,  the  use  of  carbolic  acid  as  a  protection  against  hog 
cholera  is  of  little  or  no  value,  since  it  is  known  that  the 
organism  will  live  for  months  in  the  presence  of  one  half 
of  one  per  cent,  of  this  substance  which  is  so  effective  in  the 
destruction  of  many  disease-producing  organisms. 

Each  class  of  disinfectants  has  its  advantages  and  dis- 
advantages. A  particular  class  can  be  used  to  advantage 
under  certain  conditions,  while,  under  other  conditions,  its 
use  may  be  of  little  value. 

Lime.— In  the  manufacture  of  lime,  the  limestone,  which 
is  a  carbonate  of  lime,  is  heated  to  drive  off  the  carbon- 
dioxide,  forming  calcium  oxide,  which  on  exposure  to  the 
air  gradually  combines,  with  the  carbon-dioxide  in  the  air 
to  form  the  carbonate  again,  or  air-slaked  lime.  If  the 
quick  or  stone  lime,  as  it  is  often  called,  is  treated  with  six 
parts  of  water  to  ten  of  lime,  a  dry  white  powder  will  be 
obtained,  called  hydrate  of  lime  or  water-slaked  lime.  The 
water-slaked  lime  resembles  air-slaked  lime  in  appearance, 
but  not  in  composition,  as  can  be  determined  by  placing  a 
little  of  each  on  the  tongue.  The  air-slaked  lime  has  a 
chalky  feel  and  taste,  while  the  water-slaked  causes  the 
tongue  to  burn.  It  has  caustic  and  disinfecting  properties, 
while  the  air-slaked  has  no  value  whatever  as  a  disinfectant. 

Lime  is  one  of  the  best  disinfectants  that  can  be  used  on 
the  farm  for  many  purposes.  The  dry  powder,  produced 
when  a  proper  amount  of  water  is  added  to  the  lime,  can  be 
used  or  it  can  be  applied  to  the  walls  and  ceilings  in  the 
form  of  whitewash.  The  whitewash  has  a  germicidal  ac- 
tion, as  well  as  a  mechanical  incrusting  effect,  thus  placing 
the  organisms  under  such  conditions  that  they  can  not  exist 
for  any  length  of  time.  It  makes  the  stables  lighter  and 
cleaner  than  would  otherwise  be  the  case.  If  the  white- 
wash is  prepared  from  good  lime  and  properly  applied,  it 


356  AGRICULTURAL  BACTERIOLOGY 

is  probably  as  effective  a  disinfecting  agent  as  can  be  used 
to  advantage  in  ordinary  stable  disinfection.  It  can  be 
made  more  effective  by  the  addition  of  carbolic  acid  or 
chloride  of  lime. 

In  all  disinfecting  processes  it  is  essential  to  use  plenty 
of  the  agent.  The  cheapness  of  lime  is  thus  an  advantage, 
as  is  the  ease  with  which  it  can  be  procured.  It  is  also  to 
be  recommended  when  carcasses  of  animals  that  have  died 
from  transmissible  diseases  must  be  buried  instead  of  being 
burned.  In  such  cases  the  carcass  should  be  well  covered 
with  lime,  and  then  the  dirt  returned  to  the  excavation. 

Carbolic  acid. — Carbolic  acid  is  prepared  from  coal-tar 
and  is  sold  in  the  form  of  white  crystals  which  melt  below 
the  boiling-point  of  water,  and  which  remain  liquid  on  the 
addition  of  5  per  cent,  of  water  to  the  melted  acid.  It  is 
used  as  a  disinfectant  in  solutions  containing  from  1  to  5 
per  cent,  of  the  pure  acid.  Its  action  is  not  greatly  re- 
tarded by  the  presence  of  organic  matter,  as  is  the  ease 
with  so  many  other  disinfectants;  hence  it  can  be  used  for 
the  disinfection  of  feces  from  typhoid  patients,  and  the 
treatment  of  sputum  of  tubercular  people. 

Carbolic  acid,  or  phenol  as  it  is  often  called,  does  not 
find  wide  use  on  the  farm,  because  of  its  expense,  its  cor- 
rosive action  on  the  skin,  and  its  poisonous  properties. 

Coal-tar  disinfectants. — After  the  carbolic  acid  has  been 
removed  from  coal-tar,  the  residue  still  contains  substances 
that  have  a  disinfecting  action.  From  this  residue  there  is 
now  prepared  a  great  number  of  disinfectants  commonly 
known  as  coal-tar-  or  cresol  disinfeictants,  a  term  that  ap- 
pears in  the  name  of  many  of  the  proprietary  compounds, 
such  as  kresol,  kreso,  kresolig.  The  value  of  these  com 
pounds  varies  widely.  Some  are  about  equal  to  carbolic 
acid,  while  others  are  ten  times  as  effective.  The  great 
majority  are  from  two  to  three  times  as  effective  as  phenol 


DISINFECTION  357 

and  are  used  in  solutions  containing  from  1  to  3  per  cent, 
of  the  agent.  They  are  less  corrosive  and  less  poisonous 
than  phenol,  and  can  be  used  as  a  dip  for  the  destruction 
of  insects  on  animals.  They  are  usually  composed  of  the 
creosote  oil  and  soap,  and  when  mixed  with  water  form  a 
milky  emulsion  that  is  very  permanent.  They  can  be  em- 
ployed in  widely  varying  concentrations,  and  their  action 
is,  as  a  rule,  not  greatly  impaired  by  the  presence  of  or- 
ganic matter.  Only  soft  or  rain  water  should  be  used  to 
dilute  the  coal-tar  disinfectants,  because  the  salts  present 
in  hard  water  may  materially  reduce  the  disinfecting  action. 
They  are  undoubtedly  the  best  class  of  disinfectants  for 
common  use  on  the  farm,  especially  in  the  treatment  of 
animals. 

Formaldehyde. — This  important  disinfectant  is  sold  in 
the  form  of  a  40  per  cent,  solution  of  the  gas  dissolved  in 
water,  and  is  usually  called  formalin.  Its  widest  use  on  the 
farm  is  in  the  disinfection  of  closed  spaces  by  setting  free 
the  gas  from  the  liquid,  as  will  be  described  later,  and  for 
the  destruction  of  smut  on  seed  grains  and  scab  on  seed 
potatoes. 

Corrosive  sublimate. — This  compound,  frequently  known 
as  bichloride  of  mercury,  is  one  of  the  strongest  disinfect- 
ants known.  Its  disadvantages  are  its  poisonous  properties 
and  its  greatly  decreased  action  in  the  presence  of  organic 
matter  such  as  manure.  It  also  has  a  corrosive  action  on 
metals,  and  is  irritating  to  the  tissues.  It  can  be  used  to 
advantage  in  many  places  as  a  wash  or  as  a  spray  on  walls. 
For  this  purpose  it  is  used  in  a  one  to  one  thousand  solu- 
tion, or  one  ounce  of  the  salt  to  eight  gallons  of  water. 

Sulphur. — AVhen  sulphur  is  burned,  irritating  fumes  are 
formed.  When  moisture  is  present  in  the  air,  sulphurous 
acid  is  formed  which  possesses  a  considerable  disinfecting 
action.     It  is  used  in  the  place  of  formaldehyde  as  a  gaseous 


358  AGRICULTURAL  BACTERIOLOGY 

disinfectant  for  such  closed  spaces  as  refrigerators  and 
other  rooms  in  which  the  bleaching  action  of  the  sulphur 
will  be  of  no  importance.  It  can  not,  as  a  rule,  be  used  in 
furnished  rooms  because  of  this  property,  which  formalde- 
hyde does  not  possess. 

Calcium  hypochlorite. — Bleaching  pow'der  or  calcium 
hypochlorite  has  long  been  used  as  a  disinfectant  and  de- 
odorant. Under  certain  conditions  it  is  one  of  the  most 
effective  that  can  be  employed,  as  for  example  in  the  treat- 
ment of  water  and  sewage.  Many  cities  draw  their  water 
supplies  from  sources  that  may  become  contaminated  with 
typhoid  bacilli.  It  has  been  found  that  the  addition  of 
minute  quantities  of  bleaching  powder  is  sufficient  to  de- 
stroy the  typhoid  organism. 

Calcium  hypochlorite  finds  its  widest  use  as  a  deodorant 
for  use  in  cellars,  privies,  and  similar  places.  For  these 
purposes  the  dry  powder  is  usually  employed. 

It  can  be  used  for  the  treatment  of  cisterns  in  which  a 
large  amount  of  organic  matter  has  been  carried  by  the 
wash  from  the  roofs.  During  the  warm  weather  the  de- 
composition of  the  organic  matter  may  be  so  marked  as  to 
impart  a  disagreeable  odor  to  the  water,  which  can  be  over- 
come by  the  addition  of  a  solution  of  bleaching  powder. 
The  amount  to  be  added  will  depend  on  the  quantity  of  or- 
ganic matter  in  the  water.  It  should  be  added  in  small 
quantities,  as  an  excess  will  impart  the  characteristic  odor 
of  the  hypochlorite  to  the  water. 

Ferrous  sulphate  and  copper  sulphate. — These  sub- 
stances, commonly  known  as  green  and  blue  vitriol,  have 
been  widely  used  as  disinfectants  in  the  past. 

It  is  now  known  that  they  are  almost  worthless  and 
should  be  discarded  in  favor  of  some  one  of  the  efficient 
disinfectants. 

Disinfection. — The  choice  of  a  disinfectant  for  any  par- 


DISINFECTION  359 

ticular  purpose  will  depend  on  the  conditions  under  which 
it  is  to  be  used.  If  the  room  to  be  treated  is  so  constructed 
that  it  can  be  made  tight  enougrh  to  retain  the  gas  for  some 
hours,  the  use  of  formalin  or  sulphur  is  to  be  recommended. 
The  gas  penetrates  to  every  portion  of  the  room,  into  cracks 
and  crevices  into  which  it  is  difficult  to-  force  a  liquid.  Gas 
will  not  easily  penetrate  layers  of  clothing  and  bedding, 
so  that  the  treatment  of  a  living-room  or  bedroom  with  a 
gaseous  disinfectant  will  often  not  accomplish  what  many 
conceive  it  will  do.  For  the  treatment  of  surfaces  to  which 
a  liquid  can  not  be  applied  it  is  of  the  greatest  value. 

The  room  to  be  treated  should  be  made  as  tight  as  pos- 
sible by  pasting  paper  over  the  window  and  door  cracks. 
The  gas  can  be  liberated  from  the  liquid  by  the  use  of  per- 
manganate of  potash.  One  pound  of  formalin  and  one  half 
pound  of  permanganate  will  be  needed  for  each  thousand 
cubic  feet  to  be  treated.  The  permanganate  is  placed  in 
a  large  pail  and  the  formalin  poured  over  it.  A  violent 
chemical  action  results,  and  a  portion  of  the  formaldehyde 
is  set  free.  The  room  should  be  warm  and  the  air  moist 
to  obtain  the  best  results.  The  room  should  be  opened 
for  twenty-four  hours.  The  gas  has  no  harmful  action  on 
objects  except  those  of  delicate  leather. 

If  sulphur  is  used,  five  pounds  must  be  employed  for  each 
thousand  cubic  feet.  The  sulphur  should  be  placed  in  an 
iron  vessel,  which  should  be  set  in  a  pan  of  water  so  that 
the  heat  will  evaporate  a  portion  of  the  water,  for  it  is 
essential  to  have  a  considerable  amount  of  moisture  in  the 
air  if  the  sulphur  is  to  prove  effective.  The  powdered  sul- 
phur is  ignited  by  making  a  depression  in  the  center  of  the 
pile  and  adding  a  small  amount  of  kerosene,  which  is  ig- 
nited. The  room  should  remain  closed  for  twenty-four 
hours. 

Stable  disinfection. — In  the  treatment  of  stables  and 


360  AGRICULTURAL  BACTERIOLOGY 

other  places  in  which  there  is  likely  to  be  a  large  amount 
of  material,  such  as  manure  that  contains  the  harmful  or- 
ganism, the  first  step  in  the  disinfecting  process  should  be 
the  thorough  cleaning  of  the  stable  walls  and  floor,  in  order 
to  remove  as  much  as  possible  of  the  infectious  material 
and  allow  the  disinfectant  to  come  in  contact  with  the  bare 
surface  of  the  walls.  Dried  manure  is  not  easily  pene- 
trated by  the  liquids,  and  the  organic  matter  is  likely  to 
combine  with  the  disinfectant  used  and  thus  reduce  its 
action.  The  thorough  cleaning  will  remove  most  of  the 
organisms.  All  loose  woodwork  such  as  box  mangers,  etc., 
should  be  removed.  The  walls  should  be  moistened  with 
a  solution  of  corrosive  sublimate  so  as  to  prevent  dust  in 
the  subsequent  cleaning.  The  walls  and  floors  should  be 
scraped  clean,  and  the  material  removed  and  all  litter 
burned,  not  thrown  into  the  yard,  where  animals  may  have 
access  to  it. 

The  disinfectant  should  be  applied  with  a  spray-pump 
that  will  enable  one  to  reach  all  parts  and  to  force  it  into 
the  cracks.  If  whitewash  is  used,  it  should  be  strained  and 
made  thin  enough  not  to  clog  the  pump.  The  mangers 
should  be  well  scrubbed  with  a  solution  of  lye  and  then  with 
water.  A  half-hearted  job  of  disinfection  is  no  better  than 
none  at  all.  It  gives  a  fancied  but  no  real  security  against 
a  recurrence  of  the  disease. 

The  disinfection  of  yards  is  something  that  can  not  be 
done  under  ordinary  conditions.  If  a  small  yard  is  in- 
fected, a  liberal  sprinkling  with  dry,  water-slaked  lime  is 
the  best  that  can  be  accomplished.  The  disinfection  of 
fields  is  impossible.  Small  areas  may  be  limed  or  burned 
over,  but  neither  of  these  methods  is  likely  to  be  effective 
in  the  case  of  spore-bearing  organisms,  and  all  other  forms 
will  soon  die.  One  must  rely  on  natural  agencies  for  the 
destruction  of  pathogenic  organisms  that  have  been  brought 


DISINFECTION  361 

in  contact  with  the  soil  of  yards  or  fields.  It  should  be  re- 
membered that  the  patliogenie  organisms  do  not  find  condi- 
tions for  growth  in  the  soil,  and  hence  their  destruction  is 
only  a  question  of  time,  and  with  all  except  the  spore-form- 
ing bacteria  the  time  will  be  relatively  short.  Burning 
over  a  pasture  may  be  resorted  to  in  order  to  get  rid  of 
vegetable  growth  and  give  a  better  chance  for  sunlight  to 
exert  its  influence. 


INDEX 


Abortion,  contagious,  299 

Acetic  fermentation,  196 

Acid-fast  bacteria,  272,  293 

Actinomyces,  26 

Actinomycosis,  317 

Aerobic  organisms,  53 

Agar,  35 

Agirlutinin,  302 

Air,  contamination  of  milk  from, 

139 
Air,  microorganisms  in,  04 
Alcoholic  fermentation,  193 
Ammonification,  9() 
Amphitrichous   l)acteria,  22 
Anaerobic  organisms,  52 
Aniline  dyes.  10,  43 
Anthrax,  252 
Antiseptics,  56 
Antiserum,  247 
Antitoxin,  248 
Antitoxin,  tetanus,  326 
Ascospores,  28 
Ascus,  28 
Aspergilli,  30 
Auto-intoxication,  85 
Autolysis,  58 
Avian  tuberculosis,  291 
Azotobacter  chroococcum,  119 

Bacillus,    13,    20;    abortus,    301; 

botulinus,    106:    Chauvei,   263; 

coli,  166,  188;  lactis  aerogenes, 

166,  188;  pullorum,  344 
Bacteremia,  241 
Bacteria,  cell  aggregates  of,   18; 

coll  structure  of,  20;  classifica- 


363 


tion  of,  25;  determination  of 
number  of,  41;  discovery  of,  7; 
involution  forms  of,  14;  micro- 
scopical examination  of,  42; 
morphology  of,  13;  motility  of, 
21;  relation  to  animals,  85;  re- 
lation to  reaction,  53;  repro- 
duction of,  14;  size  of,  22; 
spores  of,  16;  urea-fermenting, 
98 

Bacterial  poisons,  166 

Bacterial  standards  for  milk, 
231 

Bacterium,  anthracis,  253;  Bul- 
garicum,  189,  210;  lactis  acidi, 
106,  187;  lactis  longi,  192; 
tuberculosis,  272 

Bacteroids,  129 

Benzoic  acid,  173 

Berthelot,  118 

Beyjerinck,  124 

Bichloride  of  mercury,  357 

Birds,  tuljerculosis  of,  291 

Bitter  milk,  193 

Black  leg,  263 

Bleaching  powder,  170,  358 

Boric  Acid,   173 

Bread,  199 

Broth,  preparation  of,  34 

Brown ian  movement,  43 

Butter,  abnormal  flavors  in,  207; 
control  of  flavor  of,  204,  205; 
decomposition  of,  206;  flavor 
of,  203;  renovated,  206;  sour 
cream,  203 ;  sweet  cream,  202 

Butyric  fermentation,  191 


364 


INDEX 


Cabbage  rot,  349 

Calcium,  87;  hypochlorite,  170, 
358 

Capsules,  21 

Carbohydrates,  02 

Carbolic  acid,  356 

Carbon,  cycle  of,  83 

Carbon  dioxide,  formation  of,  83 

Cellulose,  decomposition  of,  84 

Cheese,  207;  brick,  213;  camem- 
bert,  213;  cheddar,  208;  gassy, 
209;  Gorgonzola,  212;  Limbur- 
ger,  213;  mold  ripened,  212; 
Roquefort,  212;  soft,  213;  Stil- 
ton, 212;  Swiss,  210 

Chicken  cholera,  340 

Chlamydobacteriacea,  26 

Clarification  of  milk,  151 

Cladothrix,  26 

Clostridium,  17;  Pasteurianus, 
119 

Coal  tar  disinfectants,  356 

Coccus,  13 

Colonies,  39 

Commensal  microorganisms,  58 

Communicable  diseases,  239 

Concentration,  effect  on  micro- 
organisms, 49;  preservation  of 
foods  by,  171 

Condensed  milk,  172 

Conidia,  29 

Conidiophores,  29 

Copper  sulphate,  358 

Consumption,  272 

Contagious  diseases,  239 

Cornstalk  disease,  268 

Corrosive   sublimate,   357 

Cover  crops,  103 

Cream,  bacterial  content  of,  203; 
pasteurization  for  butter,  204; 
ripening  of,  205 

Cresol,  356 

Creosote,  174 

Cultures,  40 

Cycle  of  elements,  6 


Decomposition,  5,  8,  50,  61 ;  of 
foods,  136;  in  soil,  78 

Denitrification,  104 

Desiccation  of  foods,  171 

Digestion  tanks,  112 

Diphtheria,  165 

Diplococcus,  19 

Disinfectants,  56,  354;  coal  tar, 
356 

Disinfection,  351,  358';  concur- 
rent, 352;  terminal,  352 

Dosing  chamber,  114 

Earth  worms  in  soil,  76 
Eggs,  preservation  of,   178 
Endospores,  16 
Enzymes,  56 
Eubacteria,  25 

Factory  by-products,  contamina- 
tion of  milk  from,  149 

Facultative  organisms,  53 

Farcy,  320 

Fats,  62 

Feed,  contamination  of  milk 
from,  157 ;  influence  on  taste  of 
milk,  152 

Fermentation,  5,  186 

Ferrous  sulphate,  358 

Fire  blight,  347 

Fire  fanging  of  manures,  108 

Flagella,  21,  44 

Flax,  retting  of,  86 

Flies,  transmission  of  anthrax 
by,  254 

Floats,  89 

Foods,  bacteriological  control  of, 
215;  concentration  of,  171; 
contamination  of,  135,  152; 
desiccation  of,  171 ;  influence 
of  bacterial  content  on  health- 
fulness  of,  165;  organic  acids 
in,  174;  poisonous,  166;  pres- 
ervation of,  168;  preservation 
of  by  heat,   179;   preservatives 


INDEX 


365 


in,     172;     tubercle    bacilli     in, 
1.55 

Foot  and  mouth  disease,  305 
Formaldehyde,  357 
Formalin,  173 
Fowl  typhoid,  342 
Fre<'/.inor,    effect    on    micror)rgan- 
isms,  51 


Halls,  plant,  350  " 

Garget,  J58 

Gelatin,  35 

Generation  period  of  bacteria,  15 

Glanders,  320 

Gram's  stain,  45 

Haplobacteria,  24,  25 

Heat,    effect   on    microorganisms, 

52;    preservation   of    foods   by, 

179 
Hellriegel,  122 

Hemorrhagic  septicaemia,  206 
Hemp,  retting  of,  80 
Hippuric  acid,  08 
Hog  cholera,  328 
Hogs,  tuberculosis  of,  290 
House  fly,  164 
Humus,  80 
Hydrogen,  86 
Hydrogen  sulphide,  91 
Hyphae,  28 

Immunity,  242,  243;    persistence 

of,  249 
Infant  mortality,  166 
Infection,  240 
Infectious  diseases,  239 
Involution  forms,  14 
Iron  bacteria,  92 

Johne's  disease,  293 


Kefir,  190 

Koch,  10,  252,  281 

Koumiss,  195 

Leeuwenhoek,  7 

Legumes,  120 

Legume  bacteria,  groups  of,  127 

Leptothrix,  26 

Lesions,  242 

Liebig,  8,  120 

Light,  relation  of  microorgan- 
isms to,  54 

Lime,  355 

Lockjaw,  324 

Lophotrichous  bacteria,  22 

Low  temperature,  preservation  of 
foods  by,  175 

Lumpy  jaw,  317 

Lupus,  2?2 

Mallein,  323 

Manures,  107;  loss  of  organic 
matter  from,  108 

Meats,  chopped,  153 

Media,  culture,  33;  liquefiable 
solid,  35 

Mesophilic  microorganism,  51 

Metabiosis,  59 

Metachromatic  granules,  21 

Metchnikoff,  85,  190 

Methane,  86 

Microbiology,  6 

Micrococcus,  25 

Micron,  22 

Microorganisms,  distribution  of, 
63;  role  of,  3 

Microscope,  42 

Microspira,  26 

Milk,  135;  absorption  of  odors 
by,  152;  acid  fermentation  of, 
186;  bacterial  standards  for, 
231;  bitter,  193;  certified,  228, 
233;  clarifying  of,  151;  con- 
tamination of,  137,  151;  cur- 
dling   of,    187;    factors    deter- 


'S66 


INDEX 


mining  number  of  bacteria  in, 
150;  grades  of,  227;  pasteuri- 
zation of,  180,  234;  rules  for 
production  of,  216;  slimy,  192; 
straining  of,  151;  sweet  cur- 
dling of,  191;  taste  of  influ- 
enced by  feed,  152 

Milk  pails,  small  topped,  145 

Milker,  contamination  of  milk 
by,  146 

Milking  machines,  147 

Mineralization,  5 

Moisture,  relation  of  microorgan- 
isms to,  48 

Molds,  in  soil,  75;  morphology 
of,  28;  relation  to  air,  53;  re- 
lation to  reaction,  53 

Monotrichous  bacteria,  22 

Morphology,   12 

Mucors,  30 

Multicellular  organisms,  12 

Murrain,  254 

Mycelium,  29 

Nitrate  deposits,  104 

Nitric  acid,  action  on  calcium 
carbonate,  89 

Nitrification,  99 

Nitrogen,  cycle  of,  94;  fixation 
of,  117;  forms  available  to 
green  plants,  90;  loss  from 
soil,  95 

Nitrogenous  fertilizers,  availa- 
bility of,  97 

Nocardia,  20 

Nodular  disease,  293 

Oidia,  30 

Oidium  lactis,  189,  213 

Oleomargarin,  200 

Organic  acids,  174;  action  on  cal- 
cium carbonate,  89 

Oxygen,  relation  of  microorgan- 
isms to,  52 


Osmotic  pressure,  49 
Oysters,  153,  164 

Parasitic  mcroorganisms,  58 

Pasteur,  9,  179,  316 

Pasteurization,  179;  of  milk,  234 

Pathogenic  organisms,  154 

Pear  blight,  347 

Pearl  disease,  272 

Penicillia,  30 

Pepsin,  209 

Peptone,  34,  96 

Period  of  incubation,  242 

Peritrichous,  22 

Phagocytes,  243 

Phenol,  356 

Phosphates,  action  of  bacteria 
on,  89 

Phosphorus,  89 

Phthisis,  272 

Physiological  characteristics,  40 

Physiological  dryness,  48 

Pickles,  174 

Planococcus,  25 

Planosarcina,  25 

Plant  food,  available  and  un- 
available, 70;   store  in  soil,  70 

Plasmolyzed  cells,  49 

Plasmotypsis,  50 

Potassium,  90 

Preservatives,  56,  172 

Preventable  diseases,  239 

Proteins,  62;  decomposition  of, 
90 

Proteoses,  90 

Protozoa,  32,  97,  295 

Pseudomonas,  20 

Psychrophilic  microorganisms,  51 

Pure  cultures,  33;  isolations  of, 
38 

Putrefaction,  5 

Rabies,  311 

Reaction,  relation  of  microorgan- 
isms to,  53 


INDEX 


367 


Rennet,  207,  209 
Retting,  S() 
Roup,  342 

Saeeharomyctes,  2G 

Saprophytic    microorganisms,    5S 

Sarcina,  20,  25 

Sauerkraut,  174 

Scarlet  fever,  165 

Sell  i/omy  cotes,  13 

Score  card  for  dairies,  222 

Semi-permeable  membrane,  49 

Septic  tanks,  1 1 1 

Septicaemia,  241,  206 

Septic  sore  throat,  158 

Serum,  protective,  247 

Sewage  farms,  110 

Sewage  disposal,  109 

Silage,  175 

Slimy  fermentations,   192 

Smallpox,  vaccination  against, 
246 

Smoking  meats,   174 

Soil,  air  in,  73;  decomposition  in, 
78;  inoculation  of,  125;  micro- 
organisms in,  63;  moisture  in, 
72 ;  number  of  microfirganisms 
in,  75;  odor  of,  93;  reaction  of, 
74 ;  temperature  of,  74 

Spices,  174 

Spirillum,  13,  26 

Spirochaeta,  26 

Spirosoma,  26 

Splenic  fever,  254 

Spontaneous  generation,  8 

Sporangia,  29 

Sporangiaphore,  29 

Spores,  bacterial,  16,  44 

Staining  bacteria,  43 

Staphylococcus,  19 

Starters,  205 

Sterigmata,  31 

Sterile,  36 

Sterilization,  36,  37,  179,  183;  by 
filtration.  37;  by  heat,  36 


Straining  of  milk,  151 
Streptobacillus,  19 
Streptococcus,  19,  25 
Sulphates,  91;  reduction  of,  92 
Sulphur,  91,  357 
Sweet  curdling  of  milk,  191 
Symbiosis,  129 
Symptomatic  anthrax,  263 
Syrups,  172 

Taettemjolk,  192 

Temperature,  relation  of  .micro- 
organisms to,  50 

Tetanus,  324 

Tetracoccua,  20 

Texas  fever,  295 

Thermal  death  point,  52 

Thermophilic  microorganisms,  51 

Tick  fever,  296 

Torulae,  28 

Toxemia,  241 

Toxins,  241 

Transmissible  diseases,  necessity 
for  correct  diagnosis  for,  251 

Trichobacteria,  24,  26 

Tuberculosis,  269;  bovine,  155 

Tuberculin,  281 

Tuberculin  test,  283 

Tumors,  plant,  350 

Turgidity,  49 

Typhoid  carriers,  163 

Typhoid  fever,  159 

Udder,     contamination     of    milk ' 
from,  137 

Ultramicroscopic  organisms,  23 

Unicellular  organisms,  12 

Urea,  98 

Urease,  98 

Uric  acid,  98 

Utensils,  cleansing  of,  148;  con- 
tamination of  milk  from,  146 

Vaccination,  246;  against  an- 
thrax, 259;   against  black  leg, 


368 


INDEX 


265;  against  hog  cholera,  334; 

against    rabies,     315;     against 

Texas  fever,  299 
Vaccines,  246 
Vinegar,  196 
Virus,  filterable,  23 
V^itamines,  181 

Water,  ground,  salts  in,  87; 
microorganisms  in,  63;  puri- 
fication of,  169;  supplies,  con- 
tamination of,  160 

Weigert,  10 

Wells,  protection  of,  161 


Whey,     contamination     of     milk 

from,  149 ;   heating  of,  149 
White  diarrhea,  344 
Wilfarth,    122 
Wilts,  349 

Yeasts,  193,  199;  in  soil,  75; 
morphology  of,  26;  relation  to 
air,  53;  relation  to  reaction, 
53;  reproduction  of,  27; 
spores  of,  28 

Yoghurt,   190 

Zoogloea,  21 


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APR  2  8 1934 


JAN  2 

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28  B'i' 
19tt 


FEei     1363 

F£B    4REC'D 


DEC  19  1969 
[DEC    9RlC'D^ 


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UNIVERSITY  FARM  LIBRARY 


